Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8
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

$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.