Quantitative Precipitation Forecast
Issued by NWS

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000 FOUS11 KWBC 180912 QPFHSD PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 411 AM EST MON DEC 18 2017 VALID 12Z MON DEC 18 2017 - 12Z THU DEC 21 2017 DAYS 1 THROUGH 3... ...MUCH OF THE WEST... THE WESTERN PORTION OF THE COUNTRY WILL BE EXTREMELY UNSETTLED FROM THE BEGINNING OF THE WORK WEEK THROUGH MID WEEK. WIDESPREAD WINTER WEATHER IS ANTICIPATED FROM THE NWRN QUAD OF THE COUNTRY THROUGH THE INTER-MOUNTAIN WEST AND PORTION OF THE ROCKIES. A DECAYING UPPER RIDGE WILL BE REPLACED BY A STEADY LOWERING OF UPPER HEIGHTS, WHICH EVOLVES INTO AN ANOMALOUS AMPLIFIED UPPER TROUGH. THIS IMPRESSIVE UPPER TROUGH WILL DIG SOUTH AND EAST THROUGH THE PAC NW AND REACH THE GREAT BASIN BY THURS MORNING. THE FOCUS ON MON WILL BE MAINLY FROM THE MOIST ZONAL FETCH FROM THE PAC INTO THE WA AND THE NORTHERN ROCKIES, DESPITE THE UPPER TROUGH BEGINNING TO FORM OVER THE NERN PAC. EXPECT HEAVY SNOWFALL FROM OROGRAPHICS TO IMPACT THE WA CASCADES/OLYMPICS AND DOWNSTREAM INTO THE NORTHERN BITTERROOTS/ROCKIES. THEN ON TUES, WIDESPREAD HEAVY SNOWFALL IS ANTICIPATED ACROSS THE NORTHWEST, ESPECIALLY FOR THE TERRAIN. BROAD MOIST SWRLY UPPER DIFLUENT FLOW AHEAD OF THE POTENT UPPER TROUGH WILL BE IDEAL FOR SIGNIFICANT SNOWFALL ACCUMULATIONS FROM THE CASCADES OF WA/OR AND NORTHERN CA MTNS TO THE BITTERROOTS AND NORTHERN ROCKIES. FINALLY ON WED, THE UPPER TROUGH WILL PROCEED SOUTH AND EAST INTO THE GREAT BASIN BUT THE PAC MOISTURE TRANSPORT ASSOCIATED WITH THE SYSTEM WILL BEGIN TO RELAX. THUS STILL EXPECT WIDESPREAD SNOWFALL FROM NV/UT NORTH AND EAST BUT OVERALL ACCUMULATION TOTALS NOT APPROACHING THE NUMBERS FROM MON AND TUES. OVERALL IT APPEARS THE OPERATIONAL MODEL GUIDANCE AND ENSEMBLE DATA HAVE A SOLID HANDLING OF THE UPCOMING PATTERN CHANGE AND CRITICAL THERMALS. ...NORTHERN PLAINS INTO UPPER MIDWEST... A STREAK OF LIGHT TO MODERATE SNOW WILL BE POSSIBLE FROM THE NORTHERN PLAINS INTO THE UPPER MIDWEST ON TUES AND WED. AS AN ANOMALOUS UPPER TROUGH DIGS FROM THE PAC NW TO GREAT BASIN, A WEAKER SHORT WAVE FROM THE NORTHWEST TERRITORIES WILL DIG SOUTH AND EAST AND REACH ND/MN BY THURS MORNING. THIS SHORT WAVE SHOULD PRODUCE ENOUGH DYNAMIC FORCING FOR A STREAK OF WARM ADVECTION AND OVERRUNNING SNOW TO EXTEND FROM MT THROUGH ND INTO NORTHERN MN/WI. ...UPPER MS VALLEY/GREAT LAKES TO NORTHERN NEW ENGLAND... A COUPLE OF NORTHERN POLAR STREAM SHORT WAVE TROUGHS WILL SWEEP ACROSS THE NORTHERN TIER OF THE COUNTRY ON MON AND TUES. EACH FEATURE SHOULD PRODUCE POSSIBLE LIGHT ACCUMULATING SNOW FROM NORTHERN MN/UP OF MI TO UPSTATE NY AND NORTHERN NEW ENGLAND. THE MOST DYNAMIC SYSTEM OF THE TWO WILL BE THE LATTER SHORT WAVE ON TUES, A PHASING SYSTEM WITH A STRONG UPPER JET AND TRIPLE POINT LOW SLICING THROUGH NORTHERN NEW ENGLAND. THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT. MUSHER $$

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