WeatherNation Blog

PNW In For a Blow, Another Ice Storm On the Way?

HAMweather Advisory Center

HAMweather Advisory Center

The Ice Man Cometh?

The Ice Man Cometh?


Over the next few days the Pacific Northwest will be pounded yet again with heavy snow and rain as a strong pacific jet funnels moisture into the region. Heaviest snows will of course be in the mountainous regions of Washington, Northern Idaho, and Northwest Wyoming, with new accumulations reaching well above the two foot mark, and likely reaching more than three.

Also a concern with this system is flooding in the lower elevations and coastal regions of the PNW, as our Advisory Center shows, flood watches have already been posted calling for rainfall totals up to 3″ in the valleys, and up to 7″ along the coastal range.

Significant snows will not occur over the next few days for the rest of the country, however a dusting along the northern tier will occur as a weak low ambles through. The interesting story is over the weekend however.

In running our HAMweather Precipitation Type forecast product this afternoon, a possibility for another ice storm seems to be in the future. I have created a loop of the product here for you to view, that allows you control of the animation with such parameters as speed, single frame advancement, and so forth.

When viewing the product note the timestamp on the bottom of “Valid Time,” and the red swath that appears in the middle of the country late Saturday evening into Sunday morning where the animation ends. It seems the models have an idea the possibility of freezing rain / sleet / mixed precipitation is in store for the region before the weekend is out, so if you have travel plans, please stay abreast of weather conditions because if she does come together it could be an ugly situation =)

New Years Eve Midnight Forecasts for Select Cities:

  • London, England: Clear Skies, -2ºC, NE winds ~ 10kts – Full Forecast
  • New York, NY: Cloudy Skies, 29°F, Light SE Winds – Full Forecast
  • Chicago, IL: Cloudy Skies, 36°F, S Winds ~ 9mph – Full Forecast
  • Phoenix, AZ: Partly Cloudy, 55°F, Light NW Winds ~ 5mph – Full Forecast
  • Los Angeles, CA: Clear Skies, 55°F, Calm Winds – Full Forecast
  • Honolulu, HI: Partly Cloudy, 72°F, light NE winds – Full Forecast

Please be sure to view our Advisory and Radar Centers for the latest updates and developments.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick

Where is This Slop Going? Will it Snow Christmas Day?

Precipitation Type Animation - Click for Full Size

Precipitation Type Animation - Click for Full Size

Precipitation Type Forecast Christmas Morning - Click for Full Size

Precipitation Type Forecast Christmas Morning - Click for Full Size


Quick update on the transition of the precipitation pattern over America’s Heartland. For the last few days we have discussed the mix of snow, freezing rain, and liquid precipitation that will truck along the central United States to exit the country through the eastern Great Lakes and New England.

The question is, where will it snow, where will their be a mix of slop, and where will it rain?

In the early morning post we showed you a quick glance of forecast snowdepth, so for this late morning post I thought you might enjoy a look at forecast precipitation type based upon the 12z model run. There are four fields in this product, where precipitation type is defined as either liquid precipitation, snow, freezing rain, or sleet.

To view the animation select the image above left, or click here. Notice the swath of greens, reds, purples, and whites that flow in a general northeastern direction beginning in the southcentral United States (note legend on the graphic where green is rain, white snow etc). This is the progression of the surface low we have been discussing. On this morning’s 12z run, notice that the transition of liquid precipitation and snow is further north than it was, even from the 06z run. This is not an uncommon occurrence as models try to balance out the dynamics of a system, small transitory shifts with forecasts of conditions at the surface nearly always occur.

Also notice that as the first batch of weather moves through, another is forecast for the northern great plains beginning late Thursday evening to Friday morning, where a range from the upper great plains to the midwest will experience another glorious mix of winter muck =)

Of course the Pacific Northwest can’t be left out of the mix, as Christmas Eve ushers in another influx of snow that will transition through the Rockies, with rain falling from the central California Valley all along the southern coast.

Just for grins and giggle I also posted a forecast precipitation type graphic for Christmas Morning. Select the graphic at top right, or click here to see if the early morning conditions are what you want, or turn out as they were forecast! Of course if you want to see precipitation types throughout Christmas day, refer to the animation and note the valid time stamp at the bottom of the graphic.

Please be sure to view our Advisory and Radar Centers for the latest updates and developments.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick

A Quick Look at NAM – Who Will Have a White Christmas?

Forecast Snowdepth Animation - Click for Full Size

Forecast Snowdepth Animation - Click for Full Size

Forecast Snowdepth Christmas Day Valid 21z, 12/25/08

Forecast Snowdepth Christmas Day - Click for Full Size


To NAM, or not to NAM: that is the question… Weather ’tis nobler in the mind to suffer the slings and arrows of outrageous fortune, or take arms against a sea of troubles, and by opposing end them? To die.. to sleep.

Could Hamlet have been trying to determine the track of snow and rain this morning? After viewing the 06z NAM run this morning I decided to share with you the forecast snowdepth product that you have seen from time to time. Recall from previous posts (our search feature above right is an excellent tool for just such a purpose), that forecast snowdepth is essentially if new snow were to fall in some area within a forecast cycle, how much snow is likely to be left on the ground at the end of each interval within that forecast period, above that which is already existing at ground level.

The interesting part for this forecast (recall again that our WRF/NAM product contains forecast intervals of three hours out to 84 hours or 3.5 days from initialization), is the snowdepth forecast to exist along the surface low that we discussed yesterday, in addition to new snowfall from the Central Rockies to the Pacific Northwest.

Note in the animation (click here for full size or the graphic at top left) the swath of snow forecast to remain beginning in northeastern Texas on a track northeasterly through the Ohio valley. This is similar in thinking to yesterday’s outlook, but more on a line south and east to what the models were thinking. There certainly is some more hefty snow in the works for many areas!

Additionally, note how the snow ‘disappears’ as the animation progresses due to the warmer temperatures we discussed will advect into the region. I have the loop speed for the graphic a little faster than normal so you can appreciation the propagation of this system.

Because so much snow is already existing from the central Rockies to the Pacific Northwest, it may be slightly more difficult for you to discern new snowdepth patterns in the animation. This is actually a normal thing, especially for the Cascades this time of year, however new snowfall can be discerned within the region, especially along Northern California northward, and east into Wyoming.

That’s all for now, just wanted to give you a quick look at what NAM was thinking this morning. Oh, I almost forgot! You can see it in the animation, but I also saved a forecast snowdepth image for Christmas Day, valid 21z, December 25 (top right). So if you want to know who NAM thinks will have a white Christmas, just give it a click! =)

Please be sure to view our Advisory and Radar Centers for the latest updates and developments.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick

Snow, Bitter Cold, With More to Come!

WRF/NAM 2 Meter Temperature Animation

WRF/NAM 2 Meter Temperature Animation

Today's Outlook

Christmas Eve Mess

Christmas Eve Mess

Denise LaPorte's Dog Riley Gives His Thoughts on Winter

Denise LaPorte's Dog Riley Gives His Thoughts on Winter - Chicago Tribune

Christmas Lights Under The Snow Credit: Digmunster - KOMONEWS

Christmas Lights Under The Snow Credit: Digmunster - KOMONEWS

Travel was interrupted throughout many regions of the nation over the weekend from the Pacific Northwest to America’s Heartland as planes, trains, and automobiles were dealt heavy blows of snow and bitter cold, that will unfortunately continue for a bit longer.

To give an overview of temperatures through the first part of Christmas morning, we have our WRF/NAM 2 Meter Surface Temperature Animation that can be viewed full size by either clicking here, or the graphic at top left (feel free to link to, or use the image on your site as long as it remains unaltered).

The animation represents this morning’s 06z run, and at initialization clearly depicts the massive jolt of arctic air trapped in the nation’s midsection this morning. I can attest to this fact, as this morning as I went out for my morning latte and bagel, the outdoor temperature sensor on my Lincoln said “2°F,” and it definitely did not want to start. It was the scenario where the car barely turns over once, and you ask yourself: “Is a latte really worth this?” Then of course, you keep the key turned and eventually the car turns over if you’re lucky. Fortunately for me it did, and after my latte my typing speed has increased by about 40wpm =)

Watch the animation closely as the 0°F temperatures and below (purple colors) slowly stream out of the Midwest to be replaced by above freezing (note the small red TOI {temperature of interest} line that indicates the freezing mark 32°F) temperatures. Fortunately the subzero temperatures will mostly exit the country to be replaced by something a little more bearable, other than the highest elevations of the Rockies and the extreme northern Tier.

The reason warmer air will advect into the midwest is a surface low that will slowly build and move in the general direction of the Great Lakes. As usual the exact path is somewhat difficult to discern, but at this point models tend to agree that the center of the low will pass close to Chicago Proper.

When this type of setup occurs at this time of year, it brings a mixture of precipitation types, with snow on the northern edge, mixed freezing rain / sleet in the middle of a dividing line with liquid precipitation on the southern edge. In the graphic at left I have generalized the areas of projected precipitation associated with the surface low as a strong influx of gulf moisture will stream into the midwest. One key with this setup will be the marriage of surface temperatures with those aloft, as it is likely that a wide area of freezing rain and sleet will occur, however if temperatures should continue to rise as the low pushes further north, freezing rain and sleet should migrate over to all liquid precipitation.

The Pacific Northwest will continue to be bombarded through Wednesday as a nice split flow setup invades the region. Today areas all across the Rockies an upper trough will continue to lower heights as moisture rides the Pacific Train into the region spurring very heavy orographic snow along all of the mountainous terrain from the central Rockies through the Pacific Northwest, where as usual the Cascades will receive at least a foot of snow, along with the Sierras and San Juan Mountains and Colorado Rockies.

The Key for the Pacific Northwest is what is to come… again =) Most of tomorrow will be fairly quiet, however a nice split flow regime will invade on Tuesday evening through Wednesday, where snows will begin across northern California and into the Sierras, but by Wednesday the split flow will give way to an intensified trough allowing for an absurd amount of Pacific moisture to invade the region with once again well over a foot of snow for the Cascades, and a chance of snow for Seattle.

Please be sure to view our Advisory and Radar Centers for the latest updates and developments.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick

Weekend Outlook

Destructive Winter Storm

Destructive Winter Storm

The weekend will start out fairly quiet Saturday morning across the majority of the country as the Northeastern storm departs. However, things will quickly become active as the next storm system can already be seen developing across the middle part of the country where snows are falling across the northern Plains and western parts of the Great Lakes region. Additionally, light rain and mist is occurring across the Tennessee Valley along and just north of a warm front draped across the region. Very warm temperatures are expected again south of this warm front across the Deep South.

Additionally, a major and potentially destructive winter storm is starting to make its effects felt across the Pacific Northwest this morning where light snow was falling across the Portland, OR metro area. Temperatures are also bitterly cold across western Washington where lows dipped into the middle teens as far south as the Seattle metro area, with single digits farther north just east of Everett and Bellingham. The region will become very active this afternoon as the strong Pacific storm system slowly moves eastward. Overrunning precipitation ahead of the system will be in the form of snow, and very heavy snow in some locales such as the Hood Canal, the northwest Washington coast and eastern slopes of the Cascades where very high easterly up-sloping winds increase snowfall. Blizzard warnings are currently in effect for most of these areas. The Seattle metro area can expect anywhere from 3-8″ of new snowfall with the storm. Due to the extremely high pressure differences between the arctic high pressure across southern Alberta and the deep Pacific storm system,  very strong winds in excess of 70mph are likely through the Casacade passes east of Seattle, especially Snoqualmie pass. Farther south into parts of northwest Oregon, snow will likely change to sleet and/or freezing rain later Saturday evening and night as warmer southwest winds scour out some of the arctic air currently entrenched across the region. With the potential of very heavy snow, significant ice accumulation and extremely high winds, the storm has the potential to cause widespread damage and power outages across part of the region, especially western Washington and the Cascades. Winter storm warnings and blizzard warnings are currently in effect through Sunday morning.

Weekend Outlook

Weekend Outlook

Just as the Pacific Northwest weather calms down a little by late morning Sunday, the next storm will be rapidly intensifying across the Great Lakes and Northeastern regions, where heavy snows are also possible in many of the same areas that were pummeled by Friday’s storm. The major cities, especially New York City and Boston, will receive several inches of additional snowfall, with lesser amounts farther south as the snow eventually changes over to rain especially near Philadelphia and along the New Jersey coast. Windy conditions will also accompany the storm system, especially behind the front where gusts above 40mph are likely.

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