000
FXUS63 KGRR 172300
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
700 PM EDT FRI MAY 17 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 253 PM EDT FRI MAY 17 2013

A LOW PRESSURE SYSTEM DEVELOPING IN COLORADO WILL TRACK SLOWLY
TOWARD MICHIGAN THROUGH EARLY NEXT WEEK. SOUTHEAST WINDS OUT AHEAD
OF THIS SYSTEM WILL LEAD TO A WARMING TREND. ALSO MOISTURE WILL BE
ON THE INCREASE OVER TIME AND THE WEATHER WILL TURN UNSETTLED FOR
EARLY NEXT WEEK.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 253 PM EDT FRI MAY 17 2013

THE MAIN CHALLENGE DEALS WITH THE CHANCES FOR SHOWERS TONIGHT.

THE PERSISTENT AREA OF SHOWERS CONTINUES TO IMPACT THE REGION
MAINLY NORTH OF A MUSKEGON TO ALMA LINE. OTHER SHOWERS WERE
DEVELOPING OVER LAKE MI AND WERE TRACKING NORTHEAST. THE PV
ANOMALY RESPONSIBLE FOR THE SHOWERS WAS WEAKENING. IR IMAGERY
SHOWS THE CLOUD TOPS WARMING AND RADAR TRENDS SHOW THE
PRECIPITATION WEAKENING. WILL FEATURE AN EVENING PERIOD IN THE
FORECAST TO COVER THE SHOWERS ONGOING AND THEN FEATURE A LOWER POP
FOR TONIGHT.

I CONSIDERED ADDING AN AFTERNOON THUNDERSTORM TO THE FORECAST FOR
SATURDAY FOR LOCATIONS SOUTHWEST OF GRAND RAPIDS. WEAK FORCING BUT
SOME INSTABILITY IS EXPECTED. LIFTED INDEX VALUES DROP DOWN TO -2
TO -4 DEG C. THE INSTABILITY IS NOT PROGGED TO BE AS STRONG AS
TODAYS VALUES DOWN IN INDIANA WHERE THUNDERSTORMS WERE DEVELOPING.
SO WILL KEEP IT DRY FOR NOW.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 253 PM EDT FRI MAY 17 2013

FORECAST CONCERNS DURING THE LONG TERM DEAL WITH THUNDERSTORM
POTENTIAL. MEDIUM RANGE MODELS ARE LOOKING INCREASINGLY WET DURING
THE FIRST HALF OF NEXT WEEK. A SLOW MOVING NORTHERN PLAINS LOW WILL
DRIFT EAST NEXT WEEK. A STATIONARY FRONT IS PROGD TO EXTEND EWD FROM
THE LOW THROUGH NRN WISCONSIN INTO NRN LWR. WE/LL BE IN THE WARM
SECTOR SOUTH OF THE ACTIVE FRONTAL BOUNDARY. SHORT WAVES EJECTING
FROM THE ASSOCIATED UPPER LOW WILL RESULT IN SCT TO NUMEROUS
THUNDERSTORMS MON-WED. PLENTY OF INSTABILITY WILL EXIST WITH LI/S
NEAR -8C AND SBCAPE IN THE 2K-3K J/KG RANGE. SHEAR VALUES AROUND 40
KTS SUGGESTS STRONG STORMS POSSIBLE BUT NOT TOTALLY SOLD ON THE SVR
POTENTIAL YET. MOISTURE SHOULDN/T BE A LIMITING FACTOR AS A 30KT SW
FLOW WILL DRAW MOISTURE NWD FROM THE GULF. CONVECTIVE INITIATION
WILL LIKELY DEPEND ON MULTITUDE OF SHORT WAVES MOVING ACROSS THE
GREAT LAKES.

THE CONVECTIVE THREAT WILL DIMINISH AFTER WEDNESDAY AS THE SFC LOW
MOVES EAST OF THE CWA AND COOLER AND MORE STABLE NE WINDS DEVELOP.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 702 PM EDT FRI MAY 17 2013

EXPECT VFR CIGS/VSBY THROUGH SATURDAY AFTERNOON AT ALL TAF SITES.

LAYERED CLOUDS (VFR CIGS) WILL PERSIST THROUGH SATURDAY
AFTERNOON. THE CLOUDS ARE THE RESULT OF MID LEVEL MOISTURE BEING
LIFTED NORTHWARD OVER A WEAK STATION FRONT SOUTH OF INTERSTATE 80.
A WEAKENING SOUTHERN STREAM SYSTEM PASSING THROUGH THE LOWER OHIO
VALLEY (SHOWERS WITH THAT SHOULD STAY SOUTH OF INTERSTATE 80) WILL
CONTINUE TO FEED MOISTURE NORTHWARD OVER THAT STATIONARY FRONT
UNTIL IT IS EAST OF OHIO/KENTUCKY LATE IN THE DAY ON SATURDAY. LIFT
FROM THE ENTRANCE REGION OF POLAR JET OVER NORTHEAST OF LAKE
HURON IS ALSO AIDING THE DEVELOPMENT OF A EXTENSIVE AREA OF
LAYERED CLOUDS (RAIN NORTH OF ROUTE 10) OVER MICHIGAN/WISCONSIN.
BY LATE IN THE DAY SATURDAY THE SOUTHERN STREAM SYSTEM SHOULD BE
FAR ENOUGH EAST TO CUT OFF THE FEED OF MOISTURE OVER THE FRONT TO
OUR SOUTH WHILE AT THE SAME TIME THE JET ENTRANCE REGION OF THE
POLAR JET SHOULD ALSO BE FAR ENOUGH EAST SO AS TO REDUCE THE LIFT
AT MID LEVELS OVER LOWER MICHIGAN. THAT COMBINATION OF THOSE TWO
FEATURES SHOULD RESULT IN CLEARING SKIES TOWARD SATURDAY EVENING.

&&

.MARINE...
ISSUED AT 253 PM EDT FRI MAY 17 2013

GENERAL OFFSHORE FLOW WILL KEEP WAVE HEIGHTS TO A MINIMUM.
PRESSURE GRADIENT REMAINS RELATIVELY WEAK...SO WIND TO STAY UNDER SCA.


&&

.FIRE WEATHER...
ISSUED AT 253 PM EDT FRI MAY 17 2013

HUMIDITY LEVELS SHOULD DROP OFF INTO THE 25 TO 30 PERCENT RANGE
SOUTH OF GRAND RAPIDS THROUGH ABOUT 23Z. THIS COMBINED WITH TEMPS
IN THE 70S WILL LEAD TO AN ELEVATED FIRE DANGER RISK.

&&

.HYDROLOGY...
ISSUED AT 253 PM EDT FRI MAY 17 2013

LOCALIZED SHOWERS NOT CREATING MUCH QPF THIS
AFTERNOON...GENERALLY UNDER A TENTH OF AN INCH. A HIGHER RISK FOR
HEAVIER SHOWERS WILL ARRIVE BY MONDAY AS GULF MOISTURE WORKS ITS
WAY INTO THE AREA.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.
&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...93
AVIATION...WDM
FIRE WEATHER...MJS
HYDROLOGY...MJS
MARINE...MJS