Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2
000
FXUS02 KWBC 191534
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1033 AM EST MON FEB 19 2018

VALID 12Z THU FEB 22 2018 - 12Z MON FEB 26 2018

...ARCTIC AIR DROPS THROUGH THE WEST/CENTRAL U.S. WITH RECORD
WARMTH ACROSS THE EAST...
...CLASHING AIR MASSES SET STAGE FOR AN ARKLATEX TO TN/OH VALLEYS
HEAVY RAINFALL THREAT...


...PATTERN OVERVIEW...

VERY STRONG UPPER RIDGING OFF THE CAROLINAS WILL ONLY SLOWLY
WEAKEN THROUGH THE PERIOD WITH TROUGHING REMAINING IN THE WESTERN
CONUS. A LEAD SHORTWAVE WILL LIFT OUT OF THE FOUR CORNERS REGION
THIS WEEKEND INTO THE GREAT LAKES AND NORTHEAST SUN/MON WITH
ANOTHER PACIFIC SYSTEM DROPPING NEARING THE WEST COAST BY NEXT
MONDAY. A WAVY FRONTAL BOUNDARY IN THE EAST WILL BE THE FOCUS FOR
LOCALLY HEAVY RAINFALL THROUGH THE WEEK INTO THE START OF THE
WEEKEND WITH WARM SPRING-LIKE TEMPERATURES TO ITS SOUTH AND WELL
BELOW AVERAGE TEMPERATURES TO ITS NORTH.


...MODEL GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES...

LATEST MODEL GUIDANCE SHOWED GOOD OVERALL AGREEMENT ON THE PATTERN
TO START ON THURSDAY, WITH THE GUIDANCE AGAIN TRENDING A BIT
FARTHER SOUTH WITH THE FRONT THROUGH VIRGINIA. IN THE WEST, UKMET
BECAME THE FIRST TO DEPART FROM THE GOOD DETERMINISTIC CONSENSUS
WITH A QUICKER EJECTION OF THE SHORTWAVE THAN THE GFS RUNS,
FOLLOWED BY THE SLOWER ECMWF/CANADIAN. BLEND OF THOSE CAMPS WAS
THE PREFERENCE AS THAT SHORTWAVE LIFTED NORTHEASTWARD (THOUGH LESS
WEIGHT TO THE SLOWER CANADIAN GIVEN THE PROGRESSIVE SW FLOW). BY
THE WEEKEND, GFS RUNS WERE DEEPER WITH HEIGHT FALLS OUT OF THE
NORTHEAST PACIFIC (GULF OF ALASKA) AND WAS FARTHER SW THAN THE
ECMWF ENSEMBLES. BASED MOST OF THE REST OF THE FORECAST ON THE 00Z
ECMWF/ECMWF ENSEMBLE MEAN AND 06Z GEFS MEAN, THOUGH KEPT A SMALL
PORTION OF THE GFS IN TO HELP RESOLVE SOME DETAIL IN THE EAST.
THIS ALLOWED HEIGHTS TO BRIEFLY REBOUND THROUGH THE FOUR CORNERS
REGION SUN/MON IN BETWEEN THE TWO SHORTWAVES.


FRACASSO


...WEATHER HIGHLIGHTS/THREATS...

WITH SEVERAL INCHES OF RAINFALL OCCURRING BEFORE 22/1200Z...THERE
MAY ALREADY BE ONGOING HYDROLOGIC ISSUES ANYWHERE FROM THE
ARKLATEX INTO THE MO/OH RIVER VALLEYS. THE CURRENT DAY 1-3
PRECIPITATION FORECAST HIGHLIGHTS AN AXIS OF 4 TO 6 INCHES FROM
NORTHEAST TX INTO SOUTHERN AR. BASED ON THE LATEST OUTPUT FROM THE
GLOBAL GUIDANCE...ADDITIONAL RAINFALL IS LIKELY OVER THESE REGIONS
ON THURSDAY THROUGH PERHAPS SATURDAY. INTENSE 850-700 MB MOISTURE
FLUX ANOMALIES WILL OVERLAP THIS REGION WITH DEPARTURES FROM
AVERAGE LIKELY IN THE 3 TO 4 STANDARD DEVIATIONS RANGE AT TIMES.
WITH THIS EXPECTATION OF MORE INTENSE RAINFALL AND WET ANTECEDENT
CONDITIONS...ADDITIONAL FLOOD AND FLASH FLOOD CONCERNS WILL BE A
MAJOR ISSUE. WHILE DETAILS WILL CHANGE IN THE UPCOMING DAYS...THE
THREAT SHOULD REMAIN INTO THE WEEKEND AND EVEN BEYOND GIVEN ANY
APPRECIABLE RIVER LEVEL RISES.

OTHER AREAS OF INTEREST WILL BE ALONG THE NORTHERN EXTENT OF THIS
PRECIPITATION SHIELD AS SNOW COULD FALL ANYWHERE FROM THE UPPER
MIDWEST/GREAT LAKES AND INTO SECTIONS OF INTERIOR NORTHEAST. AND
ACROSS THE WESTERN U.S...WHILE THE SYSTEMS ARE NOT FORECAST TO TAP
INTO THE BEST PACIFIC MOISTURE FEEDS...IT SHOULD REMAIN UNSETTLED
OVER THE REGION. IT DOES APPEAR SNOW LEVELS WILL DROP CONSIDERABLY
AS 1000-500 THICKNESSES DECREASE MARKEDLY WITH A COUPLE OF THESE
SYSTEMS. THIS WOULD ULTIMATELY SPREAD SNOW INTO MANY OF THE LOWER
ELEVATIONS ACROSS THE NORTHWESTERN U.S.

WITH HIGH AMPLITUDE FLOW IN PLAY...A MARKED TEMPERATURE CONTRAST
WILL EXIST ALONG THIS MENTIONED BAROCLINIC ZONE. WITHIN THE
EXPANSIVE WARM SECTOR...THERE WILL BE MANY CHANCES TO BREAK DAILY
TEMPERATURE RECORDS FROM THE DEEP SOUTH ALL THE WAY INTO NEW
ENGLAND...PARTICULARLY ON THURSDAY. MORE SPECIFICALLY...IT WILL BE
THE WARM OVERNIGHT MINIMA THAT SHOULD BE THE STORY.  AS HIGH
THETA-E AIR SHOULD CONTINUE TO BE TRANSPORTED WITHIN AN ACTIVE
PLUME OF GULF MOISTURE...OVERNIGHT LOWS WILL BE AFFECTED GIVEN
OVERCAST/RAINY CONDITIONS. DEPARTURES FROM CLIMATOLOGY SHOULD
CONTINUE TO BE AROUND 15 TO 25 DEGREES WITH BELOW FREEZING
TEMPERATURES NOT BEING FOUND UNTIL INTERIOR NEW ENGLAND AND AT
TIMES THE LOWER GREAT LAKES.

ACROSS THE WESTERN/CENTRAL U.S...IT WILL REMAIN QUITE COLD AS
MODIFIED ARCTIC AIR INFILTRATES THE REGION. GENERALLY
SPEAKING...DEPARTURES FROM AVERAGE WILL BE AROUND 1O TO 20 DEGREES
ALTHOUGH SLIGHTLY HIGHER NUMBERS ARE EXPECTED ACROSS THE NORTHERN
ROCKIES AS HIGHS STRUGGLE TO ESCAPE THE SINGLE DIGITS AND TEENS ON
THURSDAY/FRIDAY. GIVEN EXPECTED LOWS BELOW FREEZING ALONG A
SIGNIFICANT CHUNK OF THE WEST COAST...MANY REGIONS CAN EXPECT A
FREEZE TO OCCUR. THIS COULD EVEN AFFECT SECTIONS OF THE CA COAST
ALTHOUGH THE MAJOR CITY CENTERS INCLUDING SAN FRANCISCO...LOS
ANGELES...AND SAN DIEGO WILL ESCAPE THIS.


RUBIN-OSTER


$$





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