All Weather News

Wintry Blast to Slam Northern Rockies

10 Oct 2008, 5:22 pm

Recall last Monday’s post about snow for this weekend. It is always fun to compare the ‘accuracy’ of medium range forecast models to shorter range forecast models, and of course forecast verification after the event.

As of this writing winter storm watches, warnings, and even a blizzard watch have been posted for the northern Rockies with emphasis on most of the state of Wyoming, southern Montana, and eastern Idaho. The current blizzard watch issued by the NWS office out of Riverton, Wyoming is as follows:



URGENT – WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE RIVERTON WY
1219 PM MDT FRI OCT 10 2008

…A MAJOR EARLY SEASON SNOW STORM IS POISED TO IMPACT MUCH OF WESTERN AND CENTRAL WYOMING FRIDAY THROUGH AT LEAST SATURDAY NIGHT…

.AN ORGANIZING STORM ACROSS THE GREAT BASIN WILL TRACK SLOWLY TOWARD WYOMING. COPIOUS AMOUNTS OF SNOWFALL WILL LIKELY FALL TODAY THROUGH SATURDAY NIGHT AND ACROSS THE FAR NORTH INTO SUNDAY MORNING. HUNTERS…TRAVELERS AND OTHERS WITH OUTSIDE INTERESTS SHOULD STAY ON TOP OF THE LATEST WEATHER FORECASTS AND ROAD CONDITIONS. AS THE HIGHWAY DEPARTMENT STATES… ICE AND SNOW…TAKE IT SLOW!

WYZ027>030-102300- /O.CON.KRIW.BZ.A.0001.081011T1200Z-081012T0600Z/
SOUTH LINCOLN COUNTY-ROCK SPRINGS AND GREEN RIVER-FLAMING GORGE-EAST SWEETWATER COUNTY-INCLUDING THE CITIES OF…KEMMERER…COKEVILLE…ROCK SPRINGS…GREEN RIVER…WAMSUTTER
1219 PM MDT FRI OCT 10 2008

…BLIZZARD WATCH REMAINS IN EFFECT FROM SATURDAY MORNING THROUGH SATURDAY EVENING…

A BLIZZARD WATCH REMAINS IN EFFECT FROM SATURDAY MORNING THROUGH SATURDAY EVENING.

THERE IS THE POTENTIAL FOR 3 TO 6 INCHES OF SNOWFALL TO OCCUR ACROSS SWEETWATER COUNTY SATURDAY AND SATURDAY EVENING ALONG WITH 4 TO 8 INCHES IN SOUTHERN LINCOLN COUNTY. IN ADDITION…VERY STRONG EAST NORTHEAST WINDS OF 35 MPH WITH GUSTS TO 55 MPH MAY CREATE ONE TO 3 FOOT DRIFTS ALONG WITH WHITE OUT CONDITIONS. TRAVEL ALONG INTERSTATE 80 AS WELL AS OTHER AREA HIGHWAYS MAY BECOME EXTREMELY TREACHEROUS. IN ADDITION…WIND CHILLS OF 10 BELOW ZERO ARE POSSIBLE.

HUNTERS…TRAVELERS AND OTHERS WITH OUTDOOR INTERESTS SHOULD PAY CLOSE ATTENTION TO THE WEATHER FORECAST. LISTEN TO NOAA WEATHER RADIO OR YOUR FAVORITE MEDIA OUTLET FOR THE LATEST FORECASTS AND WINTER STATEMENTS.

A BLIZZARD WATCH IS ISSUED WHEN SUSTAINED WINDS OF 35 MPH OR GREATER OR FREQUENT GUSTS OVER 35 MPH WILL COMBINE WITH CONSIDERABLE FALLING AND/OR BLOWING SNOW TO PRODUCE FREQUENT VISIBILITIES BELOW ONE QUARTER MILE IN THE NEXT 12 TO 48 HOURS. ROADS MAY CLOSE OR BECOME IMPASSABLE IN THESE CONDITIONS.


Total snowfall in areas other than the blizzard watch are more substantial, in the neighborhood of 8-16″ or higher, especially in the Green Mountains area, but since sustained winds are forecast to be lower with only occasional strong gusts, a blizzard watch was not issued for those regions.

A sample of how the current watch and warning situation stack up can be viewed below with our HWwarnings, and HAMrad II products.

Snapshot of HWwarnings and HAMrad II at the time of this posting
HWwarnings HAMrad II

Our HWwarnings product includes all watches and warnings issued by the various agencies, while our HAMrad II warning overlays are convective and winter storm type warnings designed to enhance the user experience as animations of various weather types are viewed overlain with current warnings.

Recall from last Monday’s post reviewing the GFS forecasts that the snow totals were less than what is currently forecast, and the affected region was southeast of what is currently forecast to occur. This is not anything out of the ordinary. We must remember that GFS was essentially successful in forecasting a snow event to occur ‘at some point’ in the future. Later iterations defined the event somewhat more succinctly, but not as effective as shorter range products which is the norm. You may wish to review this previous post about GFS guidance, as well as this post on NAM to aid in understanding model accuracies.

An example of what NAM is currently thinking as of the 18z run is included below.

NAM Guidance 18z run, October 10,2008
Static Graphic Valid Tuesday Oct. 14, 2008 Animation 3hr Intervals out 84 Hours

Recall from previous posts that the product above is forecast snowdepth. Essentially if snow were to fall in some area within a forecast cycle, how much snow would likely be left on the ground at the end of each interval within that forecast period? Additionally, if snow were existing on the ground before snowfall should occur, this would be taken into account, including melting, sublimation and so forth.

The static graphic above left represent how much snow is forecast to be remaining at 6z Tuesday, October 14, 2008 the end of the 84 HR NAM cycle. Compare that graphic to the existing warnings that are displayed above or view our HWwarnings and HAMrad II product with warning overlays to compare. Is it possible more watches and warnings will be needed as the system progresses based upon the current thoughts posed by NAM?

An exciting thing to do is view the animation product displayed above right, as it contains the snowdepth forecast at 3 hr intervals out to 84 hours or 3.5 days, quite succintly covering the timing of the event. It is exciting to view the increasing spread of snowfall over time, as well as depth changes as the system progresses. Watch the animation closely, compare to the static graphic that represents total snowfall ending 6z Tuesday, and compare to how the system progresses over time and after the event.

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

cheers,

–patrick

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