Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 231754
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1254 PM CDT THU APR 23 2015

.UPDATE...FOR 18Z AVIATION DISCUSSION BELOW

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 324 AM CDT THU APR 23 2015

EARLY MORNING WATER VAPOR IMAGERY REVEALS JUST HOW DRY THE AIR MASS
IS OVERHEAD. UPPER LOW/DEEPLY AMPLIFIED UPPER TROUGH STILL PARKED
OVER THE GREAT LAKES THIS MORNING...SO WE ARE STILL IN PREDOMINANT
NORTHWEST FLOW...WITH THIS AIRMASS BEING A RELATIVELY COOL ONE.  THE
MOISTURE ASSOCIATED WITH THE UPPER LOW HAS SLOWLY CREPT EASTWARD
WITH TIME...AS VERY DRY AIR HAS ADVECTED INTO OUR REGION FROM THE
NORTHWEST.  AT THE SURFACE...CLASSIC CANADIAN HIGH PRESSURE
CONTINUES TO PUSH IN.

WITH ALL THAT SAID...CLEAR SKIES AND RELATIVELY COOL TEMPERATURES
ARE ON TAP AGAIN FOR TODAY.  THE NORTHWEST WINDS WILL BE WEAKER THAN
YESTERDAY THOUGH...AS THE PRESSURE GRADIENT HAS WEAKENED SINCE THEN.
WITH MIXING TO 850MB LIKELY TODAY...LOWERED DEW POINTS ACROSS
WESTERN MN INTO THE SINGLE DIGITS FOR THIS AFTERNOON...WHICH WERE
ALSO OBSERVED YESTERDAY.  WITH HIGHS FORECAST IN THE MID 50S
THERE...RELATIVE HUMIDITY WILL DROP WELL INTO THE TEENS. THE WIND
THOUGH WILL BE LIGHT ACROSS WESTERN MN AS THE HIGH PRESSURE AXIS
SLIDES THROUGH DURING THE AFTERNOON.

FOR TONIGHT...SHORTWAVE WILL PUSH NORTHEAST OUT OF THE ROCKY
MOUNTAIN REGION. MID LEVEL LOW/MID LEVEL WARM AIR ADVECTION WILL
ENSUE REACHING WESTERN MN FIRST AROUND 06Z THEN ADVANCING EAST
TOWARD FRIDAY MORNING.  SO...CLOUD COVER WILL BE ON THE INCREASE
STARTING THIS EVE IN WESTERN MN AND EXPAND EASTWARD OVERNIGHT.  WE
WILL HAVE VERY DRY AIR AT THE SURFACE...BUT THE DECENT FORCING ALOFT
AND MOISTURE ADVECTION AS REFLECTED BY THE STRONG THETA-E ADVECTION
PROGGED FOR TONIGHT WILL BE ABLE TO PRODUCE GOOD ENOUGH PRECIP RATES
THAT WILL BE ABLE TO OVERCOME THE LOW LEVEL DRY AIR OVERNIGHT.
GENERALLY...EXPECT UP TO A TENTH OR TWO OF PRECIPITATION FOR CENTRAL
MN...WITH LESS IN EASTERN MN AND VERY LITTLE IF ANY IN WESTERN WI BY
12Z FRIDAY MORNING.  IN TERMS OF PRECIPITATION TYPE...WENT WITH A
MORE BROAD RAIN/SNOW MIX AS OPPOSED TO JUST LIGHT SNOW OVERNIGHT IN
CENTRAL MN.  CLOUD COVER AND WAA ALOFT WILL SPREAD IN A LITTLE
QUICKER TONIGHT...SO RAISED OVERNIGHT LOWS BY A COUPLE DEGREES. ONCE
THE CLOUD COVER ARRIVES...TEMPS LIKELY WILL HOLD NEARLY STEADY
THROUGH THE REMAINDER OF THE NIGHT. ANOTHER FACTOR IN THE P-TYPE
FORECAST IS THE FACT THAT 850MB-700MB TEMPS QUICKLY GO ABOVE
FREEZING JUST BEHIND WHAT WILL BE THE LEADING EDGE OF THE PRECIP AND
CONTINUE TO WARM THEREAFTER...SO MUCH OF THE PRECIP WILL BE FALLING
THROUGH THIS WARM NOSE OVERNIGHT. THE LEADING EDGE OF THE PRECIP MAY
BEGIN AS SNOW...BUT LATER TRANSITION TO RAIN.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 324 AM CDT THU APR 23 2015

THE UPPER AIR PATTERN ON THE 00Z GFS WAS IN MUCH BETTER AGREEMENT
WITH THE ECMWF AND CANADIAN VERSUS 24 HOURS AGO. THIS IS LEADING
TO A HIGHER CONFIDENCE FORECAST IN THE LONG TERM. THE MAIN WEATHER
MAKER REMAINS THE MID/UPPER LEVEL WAVE THAT WILL MOVE NORTHEAST
THURSDAY NIGHT AND FRIDAY FROM THE CENTRAL PLAINS AND THEN DRIFT
BACK TO THE SOUTHEAST ON SATURDAY DUE TO A MASSIVE UPPER LOW OVER
NEW ENGLAND. ALL SOLUTIONS POINT TO MEASURABLE RAIN ACROSS THE FA
FRIDAY AND FRIDAY NIGHT. RAIN AMOUNTS ARE NOT GREAT BUT A TENTH TO
A QUARTER INCH SHOULD OCCUR. THEREFORE...KEPT THE TREND GOING ON
RAISING POPS WITH LIKELY NOW COMMON...ESPECIALLY FOR THE MN CWA
WHERE 850-700MB MOISTURE TRANSPORT...MID LEVEL FRONTOGENESIS AND
DIFFERENTIAL DIVERGENCE PERSIST THE LONGEST. THERE WILL LIKELY BE
A MIX OF RAIN/SNOW EARLY FRIDAY MORNING TO THE NORTH AND EAST OF
THE TWIN CITIES.

THE WAVE WILL MOVE SOUTHEAST OF THE AREA ON SATURDAY WITH RAIN
EARLY ON ALONG THE I-90 CORRIDOR WITH DIMINISHING POPS
THEREAFTER. BECAUSE OF THE CLOUDS AND RAIN...HIGH TEMPERATURES
WILL REMAIN SOME 10 DEGREES BELOW NORMAL THROUGH SATURDAY. OUR
COLD BIAS WILL END ON SUNDAY AS RIDGING MOVES IN AND HIGH TEMPERATURES
BEGIN TO CLIMB BACK INTO THE UPPER 50S TO LOWER 60S THROUGH THE
REST OF THE LONG TERM WHICH IS MUCH CLOSER TO NORMAL. HOWEVER...
DUE TO THE DRY AIRMASS IN PLACE EARLY NEXT WEEK...LOW TEMPERATURES
WILL BE AT OR BELOW FREEZING FOR MANY AREAS OF CENTRAL MN THROUGH
WEST CENTRAL WI. SOME SMALL CHANCES FOR RAIN BEGIN TO SPREAD IN
FROM THE WEST MONDAY NIGHT AND THEN LINGER OVER THE AREA TUESDAY
AND EARLY WEDNESDAY AS THE NEXT SHORT WAVE AND WEAK SURFACE COOL
FRONT PUSH THROUGH.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1255 PM CDT THU APR 23 2015

BENIGN WEATHER WITH CLEAR SKIES AND VFR CONDITIONS INTO THIS
EVE...THEN MID/HIGH CLOUDS INCREASE FROM THE WEST THIS EVENING.
THE INITIAL SURGE OF MOISTURE/LIFT MAY BE MORE OF A VIRGA
SITUATION OVER CENTRAL MN...WITH ANY PRECIP THAT DOES MAKE IT TO
THE GROUND ACCOMPANIED BY P6SM OR GREATER VSBYS. THEREFORE...HAVE
GONE WITH VCSH MENTIONS INITIALLY AT SOME OF THE
SITES...TRANSITIONING TO PREVAILING -SHRA TOWARD THE END OF THE
PERIOD /18Z/ AS THE BETTER LIFT AND SATURATION ARRIVE. LIGHT
WEST/NORTHWEST WINDS THIS AFTERNOON BECOME VARIABLE AREA-WIDE THIS
EVE...THEN INCREASE TO AROUND OR ABOVE 10KTS OVERNIGHT AS THE
TROUGH APPROACHES.

KMSP...
EXPECTING THE RAIN TO HOLD OFF UNTIL AFTER 12Z AT THIS
TIME. COULD SEE VIRGA WITH A FEW VERY LIGHT SHOWERS AS EARLY AS
12Z...BUT THE MAIN PRECIP SHOULD HOLD OFF UNTIL 18Z.
MVFR APPEARS POSSIBLE WITH THE SHOWERS AFTER 18Z...BUT NOT
CONFIDENT ENOUGH WITH TIMING/PROBABILITY TO INCLUDE AT THIS POINT.

/OUTLOOK FOR KMSP/

SAT...VFR. SLGT CHC -RA. WINDS ENE 10-12 KT.
SUN...VFR. WINDS ENE 5-10 KT.
MON...VFR. WINDS ENE 5 KT.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

$$


SHORT TERM...SPD
LONG TERM...RAH
AVIATION...LS


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