Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 250659
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT SUN JUN 25 2017

VALID 12Z WED JUN 28 2017 - 12Z SUN JUL 2 2017

***PATTERN OVERVIEW AND MODEL PREFERENCES***

THE MEDIUM RANGE PERIOD WILL BEGIN ON WEDNESDAY WITH A QUASI-ZONAL
PATTERN ACROSS THE CONTINENTAL U.S. AS THE EASTERN U.S TROUGH AXIS
EXITS THE COAST AND LOW AMPLITUDE RIDGING ALOFT BUILDS IN.
LOWERING MID LEVEL HEIGHTS ACROSS THE WESTERN HALF OF THE NATION
IN RESPONSE TO THE DISTURBANCE MOVING EASTWARD ACROSS SOUTHERN
CANADA WILL SUPPRESS THE UPPER LEVEL RIDGE SOUTHWARD INTO MEXICO.
BY NEXT WEEKEND, UPPER LEVEL TROUGHING WILL LIKELY BECOME
ESTABLISHED OVER THE NORTH-CENTRAL U.S. ALONG WITH COOLER
TEMPERATURES AND SIGNIFICANT RAINFALL.

IN TERMS OF MODEL PREFERENCES, A BLEND OF THE OPERATIONAL UKMET,
GFS, AND ECMWF WAS INCORPORATED FOR THE FIRST HALF OF THE FORECAST
PERIOD.  NO CMC WAS USED ANYWHERE IN THE FORECAST GIVEN ITS EARLY
DEPARTURES FROM THE MODEL CONSENSUS.  IT WAS TOO AMPLIFIED WITH
THE EAST COAST TROUGH AND INDICATED LESS IN THE WAY OF TROUGHING
ACROSS THE INTERMOUNTAIN WEST COMPARED TO THE MODEL CONSENSUS.
THE GFS REMAINS A DEEPER SOLUTION ACROSS THE CENTRAL U.S. WITH
RESPECT TO THE TROUGH FROM SOUTHERN CANADA, BUT STILL CLOSE ENOUGH
TO BE INCORPORATED INTO THE FORECAST BLEND.  INCREASING
PERCENTAGES OF THE GEFS AND EC MEANS WERE USED FOR NEXT WEEKEND
WHEN UNCERTAINTIES RELATED TO MESOSCALE DETAILS BECOME MORE
SIGNIFICANT.


***SENSIBLE WEATHER***

THE UPPER LEVEL LOW MOVING EASTWARD ACROSS SOUTHERN CANADA, ALONG
WITH ITS SURFACE LOW AND TRAILING COLD FRONT, APPEARS TO BE THE
MAIN PLAYER IN TERMS OF PRECIPITATION DURING THIS PERIOD.  AS THIS
DISTURBANCE REACHES THE NORTHERN PLAINS AND UPPER MIDWEST LATER IN
THE WEEK, NUMEROUS HEAVY SHOWERS AND STORMS ARE LIKELY TO DEVELOP,
ESPECIALLY ALONG AND AHEAD OF THE TRAILING COLD FRONT AND NEAR A
SURFACE LOW.  MODELS CONTINUE TO STRONGLY ADVERTISE AN AXIS OF
HEAVY RAIN FROM EASTERN KANSAS AND NEBRASKA TOWARDS THE GREATER
CHICAGO AREA, WITH SOME SOLUTIONS INDICATING IN EXCESS OF 5 INCHES
OF RAIN ACROSS PARTS OF IOWA AND NORTHERN MISSOURI THROUGH FRIDAY.
 AREAS OF EXCESSIVE RAINFALL CAPABLE OF PRODUCING FLASH FLOODING
APPEAR INCREASINGLY LIKELY, AND FUTURE EXCESSIVE RAINFALL OUTLOOKS
FROM WPC WILL HAVE ADDITIONAL INFORMATION AS THE EVENT ENTERS THE
SHORT-RANGE PERIOD.  IT IS ALSO INTERESTING TO NOTE THAT MONSOONAL
MOISTURE IS BEGINNING TO INCREASE OVER WESTERN MEXICO, AND THE
NORTHERN EXTENT OF THIS MAY REACH INTO SOUTHEAST ARIZONA AND
SOUTHWEST NEW MEXICO AT TIMES.

HOT WEATHER IS FORECAST TO CONTINUE FOR THE LOWER ELEVATIONS OF
THE DESERT SOUTHWEST, ALBEIT SLIGHTLY COOLER COMPARED TO THE
EXTREME VALUES OF LATE OWING TO THE WEAKENING OF THE UPPER RIDGE.
A HIGH QUALITY AIRMASS WITH PLEASANT TEMPERATURES IS EXPECTED
ACROSS THE EASTERN U.S. FOR THE MIDDLE OF THE WEEK WITH A CANADIAN
SURFACE HIGH OVER THE REGION.  HOWEVER, THE HEAT AND HUMIDITY IS
FORECAST TO RETURN TO CLOSE OUT THE WORK WEEK WITH SOUTHERLY FLOW
INCREASING AHEAD OF THE APPROACHING FRONTAL SYSTEM TO THE WEST.

D. HAMRICK

$$




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