EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1051 AM EDT WED MAY 22 2013

VALID 12Z SAT MAY 25 2013 - 12Z WED MAY 29 2013


THE GLOBAL NUMERICAL MODELS CONTINUE TO SHOW HIGH-LATITUDE
BLOCKING FROM THE NORTHEAST PACIFIC TO THE NORTH ATLANTIC THROUGH
THE MEDIUM RANGE. AN OMEGA-ISH FLOW CONFIGURATION IS EXPECTED TO
DOMINATE NORTH AMERICA INTO EARLY DAY 5--WITH UPPER LOWS NEAR
VANCOUVER ISLAND AND ASTRIDE THE SAINT LAWRENCE RIVER. BY LATE DAY
6, AN UNSEASONABLY STRONG JET IS PROGGED TO PLUNGE INTO THE
PACIFIC NORTHWEST COAST ALONG 40N, WHICH WILL INDUCE LARGE HEIGHT
RISES OVER MUCH OF THE EASTERN UNITED STATES THEREAFTER. THE
ENSEMBLE MEANS FROM THE GFS AND BOTH THE CANADIAN AND EUROPEAN
CENTRES AGREE ON THIS THEME, WITH THE DETERMINISTIC MODELS
OFFERING "NOISY"--IE UNRELIABLE--DEPICTIONS OF THE PATTERN CHANGE.
THE EUROPEAN CENTRE ENSEMBLE MEAN FORMED THE BACKBONE OF THE
MANUAL FRONTS AND PRESSURES DAYS 3-7, WITH ITS STABILITY OVER THE
PAST SEVERAL MODEL CYCLES THE MAJOR FACTOR IN ITS PREFERENCE OVER
THE OTHER GUIDANCE.

SUBSTANTIAL NEGATIVE DEPARTURES FROM NORMAL IN TEMPERATURE ARE
INDICATED FOR MUCH OF THE EAST THIS PERIOD, WITH MORE MODEST
NEGATIVE DEPARTURES IN THE PACIFIC NORTHWEST. THE BULK OF THE
PRECIPITATION EAST OF THE ROCKIES WILL FOCUS ALONG AND NORTH OF
THE POLAR FRONT. OVER THE NORTHWEST, PRECIPITATION WILL BE LESS
ORGANIZED UNTIL DAY 7, WHEN THE STRONG ONSHORE PUSH ASSOCIATED
WITH THE NEW JET WRINGS OUT PACIFIC MOISTURE FROM NORTHERN
CALIFORNIA THROUGH OREGON AND WASHINGTON.


CISCO