Prognostic Meteorological Discussion
Issued by NWS

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000 FXUS02 KWBC 081601 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1100 AM EST THU DEC 08 2016 VALID 12Z SUN DEC 11 2016 - 12Z THU DEC 15 2016 ...ARCTIC AIR TO SURGE INTO THE LOWER 48 NEXT WEEK... ...PATTERN OVERVIEW... A MIDDLE/UPPER-TROPOSPHERIC CLOSED LOW REMAINS FORECAST TO DROP SOUTHWARD FROM NUNAVUT THIS WEEKEND AND THEN TURN EASTWARD THROUGH SOUTHERN CANADA DURING THE MIDDLE OF THE NEXT WEEK. UNDERNEATH...UNCERTAIN NORTHERN PACIFIC SHORTWAVE ENERGIES PROGRESS FROM THE NWRN US/CA THROUGH THE INTERMOUNTAIN W/ROCKIES SUN INTO MON IN GENERAL LOWER 48 ZONAL FLOW LEADING TO SOME CENTRAL US AMPLIFICATION AHEAD OF THE NRN STREAM CANADIAN UPPER LOW. A BROAD CYCLONIC CIRCULATION WITH UNCERTAIN NRN STREAM INFLUENCE ALOFT SHOULD THEN ENCOMPASS THE EASTERN HALF OF THE LOWER 48 INTO NEXT WED/THU AS ADDITIONAL PACIFIC IMPULSES WORK BACK TO THE WRN STATES. ...GUIDANCE PREFERENCES... GUIDANCE QUESTIONS ARISE WITH HOW PACIFIC SHORTWAVES ZIP THROUGH THE FLOW ACROSS THE CONUS NEXT SUN-MON AHEAD OF THE INTENSE COLD SURGE FROM THE NORTH. BIGGER QUESTIONS INTO MIDWEEK CONCERN THE EXTENT OF NRN STREAM HEIGHT FALLS WORKING INTO THE NWRN US ALONG WITH POTENTIALLY MORE ERNEST NRN AND SRN STREAM TROUGH HEIGHT FALLS/PHASING DOWNSTREAM OVER THE E-CENTRAL US. GUIDANCE HAS NOT BEEN VERY CONSISTENT WITH EMBEDDED IMPULSE TIMING/SFC DEFINITION OUT FROM SHORT RANGE TIME SCALES INTO EARLY NEXT WEEK LENDING A COMPOSITE SOLUTION. HOWEVER...CAN THE ARCTIC SURGE SPIN UP DEEPENING LOW PRESSURE ALONG THIS LEADING FRONT TO SLOW ITS PROGRESSION EASTWARD NEXT TUE/WED AS CHAMPIONED BY RECENT GFS RUNS? WPC PROGS DO NOT EMPHASIZE THIS HEAVIER RAIN AND NORTHWARD WINTER WEATHER THREAT AT THIS POINT...BUT IT REMAINS POSSIBLE CONSIDERING NRN STREAM AMPLITUDE EXTENDING THROUGH ALASKA. ...WEATHER HIGHLIGHTS/THREATS... PERSISTENT WEST TO EAST MID-LEVEL FLOW WILL KEEP THE WESTERN REGION ACTIVE, ESPECIALLY OVER NORTHERN CALIFORNIA NORTHWARD ALONG THE COASTAL RANGE AND CASCADES. ADDITIONAL UPLIFT VIA THE ARCTIC BOUNDARY MOVING OUT OF MONTANA WILL PROVIDE ANOTHER MECHANISM FOR SNOWFALL OVER THE BITTERROOTS AND SAWTOOTH RANGE AND BROAD VICINITY. GENERALLY ABOVE AVERAGE TEMPERATURES WILL CONTINUE FOR THE SOUTHWESTERN FIFTH OF THE CONUS (CA/NV/UT/AZ AND WESTERN CO/NM). WITH THE FORECAST ARCTIC SURGE COMING OUT OF SOUTHWEST CANADA INTO THE N-CENTRAL US...AN IMPRESSIVE AREA OF WELL BELOW AVERAGE TEMPERATURES WILL RUSH SOUTHWARD AND EASTWARD FROM THE NORTHERN HIGH PLAINS THROUGH THE MIDWEST AND EVENTUALLY TO THE EAST COAST BY WED/THU NEXT WEEK. TEMPERATURES MAY BE 20-30 DEGREES BELOW AVERAGE AND MAY FLIRT WITH SOME RECORDS (PERHAPS RECORD LOW MAXIMA) THOUGH THE LONGER PERIOD STATIONS GENERALLY HAVE SOME VERY COLD RECORDS BY NOW (MID-DECEMBER). NW FLOW AND COLD AIR OVER THE GREAT LAKES SHOULD SUPPORT A MULTI-DAY LAKE EFFECT EVENT FROM MICHIGAN EASTWARD THROUGH NE OHIO/NW PA INTO WESTERN/CENTRAL NY INCLUDING THE TUG HILL PLATEAU. TRACK OF THE EXITING SFC LOW AND INCOMING SFC HIGH WILL DETERMINE WHO SEES THE MOST SNOW...BUT SETUP LOOKS GOOD PROVIDED ENOUGH MOISTURE CAN BE WRUNG OUT IN THE OVERALL DRY/COLD AIRMASS. GLOBAL MODELS/ENSEMBLES GENERALLY HAVE A GREEN LIGHT FOR AT LEAST LIGHT-MODERATE SNOW NEXT TUE-THU (AND PERHAPS BEYOND). SCHICHTEL $$

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