Prognostic Meteorological Discussion
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652
FXUS02 KWBC 051601
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EST MON DEC 05 2016

VALID 12Z THU DEC 08 2016 - 12Z MON DEC 12 2016

...OVERVIEW...

THE MEDIUM-RANGE PERIOD WILL BEGIN WITH THE FIRST OUTBREAK OF
ARCTIC AIR WELL UNDER WAY INTO THE MID-SECTION OF THE
COUNTRY...AND SHOULD CONTINUE TO SPREAD EASTWARD INTO THE ENTIRE
EAST COAST ON SATURDAY.  AS THE ARCTIC AIR MODERATES THIS WEEKEND
AND PACIFIC MOISTURE PENETRATES FARTHER INLAND ACROSS THE WESTERN
U.S. UNDER STRONG UPPER-LEVEL WESTERLIES...MODELS ARE INCREASINGLY
POINTING TOWARD A LOW-AMPLITUDE ZONAL UPPER-LEVEL FLOW WITH A
SPLIT FRONTAL REGIME SETTING UP ACROSS THE U.S. BY EARLY NEXT WEEK.


...GUIDANCE EVALUATION/PREFERENCES...

MODELS HAVE FINALLY COME INTO UNANIMOUS AGREEMENT ON THE SPEED OF
THE ARCTIC AIR MASS SPREADING ACROSS THE EASTERN THIRD OF THE
COUNTRY LATE THIS WEEK AS THE ECMWF HAS SPED UP AND IS NO LONGER
INDICATING CYCLOGENESIS ON THE ARCTIC FRONT.  THEREAFTER...MODEL
GUIDANCE IS IN GOOD AGREEMENT THAT THE ARCTIC HIGH WILL MOVE OFF
THE MID-ATLANTIC COAST ON DAY 6 SUNDAY AS MOISTURE IN THE
NORTHWESTERN U.S. CONTINUES TO BRING PRECIPITATION QUICKLY ACROSS
THE NORTHERN ROCKIES INTO THE NORTHERN PLAINS BY DAY 5 SATURDAY.
THE RETREATING ARCTIC HIGH WILL BRING MOISTURE NORTHWARD FROM THE
GULF AS WELL.  THE WPC PRESSURE FIELDS WERE DERIVED USING A 70-30%
BLEND OF THE 06Z GFS AND 00Z ECMWF SOLUTIONS.

...WEATHER HIGHLIGHTS/THREATS...

COLD AIR OVER THE CNTRL U.S. ON DAY 3 THU... WITH TEMPS 15-30F
BELOW NORMAL... WILL PUSH INTO THE EAST FOR LATE THU THROUGH SAT
WITH CONSIDERABLE COVERAGE OF MINUS 10-20F ANOMALIES OVER
CNTRL-SRN AREAS.  EXPECT LESS EXTREME READINGS OVER THE
GRTLKS/NORTHEAST.  AT THE SAME TIME THE PLAINS WILL TREND WARMER
EXCEPT FOR FAR NRN AREAS WHICH MAY REMAIN WELL BELOW NORMAL INTO
AT LEAST EARLY NEXT WEEK.  BRISK AND COLD CYCLONIC FLOW ACROSS THE
GRTLKS SHOULD PROMOTE AREAS OF LAKE EFFECT SNOW DURING THU-FRI.
FROM THE WEEKEND INTO EARLY NEXT WEEK... POTENTIAL SYSTEM EMERGING
FROM THE HIGH PLAINS DURING THE WEEKEND AND RETURN FLOW AROUND
HIGH PRES TRACKING FROM THE ERN STATES INTO THE ATLC MAY BRING
SOME SNOW ACROSS THE NRN PLAINS/GRTLKS AND PSBLY INTO THE
NORTHEAST WHILE RAIN WILL BE PSBL OVER SRN AREAS OF THE E-CNTRL
U.S..  DETAIL UNCERTAINTIES SFC/ALOFT LEAD TO LOW CONFIDENCE IN
EXACT LATITUDE OF THE RAIN-SNOW LINE AT THIS TIME.

OVER THE WEST... THE MEAN PATTERN WILL FAVOR A WINDWARD FOCUS FOR
ENHANCED PCPN FROM THE PAC NW AND NRN HALF OF CA EWD INTO THE
ROCKIES.  FOR THE 5-DAY PERIOD AT LEAST SEVERAL INCHES OF LIQUID
EQUIV ARE PSBL OVER PORTIONS OF THE PAC NW COAST/CASCADES AND NRN
CA/SIERRA NEVADA RANGE WITH LESSER AMTS REACHING THE ROCKIES.
POTENTIAL REMAINS FOR A PERIOD OF STRONG WINDS OVER THE PAC NW
LATE THIS WEEK.  MODESTLY BELOW NORMAL TEMPS ON THU SHOULD RETURN
TO WITHIN A FEW DEGS ABOVE/BELOW NORMAL FOR FRI AND THEN TEND TO
LEAN MORE BELOW NORMAL THAN ABOVE THEREAFTER.

RAUSCH

$$





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