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594
FXUS63 KGRR 251613
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1215 PM EDT FRI JUL 25 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 328 AM EDT FRI JUL 25 2014
CHANCES FOR SHOWERS AND THUNDERSTORMS WILL INCREASE OVER THE WEEKEND
A COUPLE OF LOW PRESSURE SYSTEMS MOVE TOWARD THE GREAT LAKES. TODAY
WILL PARTLY TO MOSTLY SUNNY THOUGH WITH HIGHS IN THE MID TO UPPER
70S. COOLER WEATHER WILL DEVELOP NEXT WEEK AS A DEEP UPPER LOW
SETTLES OVER THE GREAT LAKES.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 328 AM EDT FRI JUL 25 2014

FORECAST CONCERNS DEAL WITH CHANCES OF SHOWERS/STORMS THROUGH THE
PERIOD.

HIGH CLOUDS WILL SPILL ACROSS THE CWA TODAY FROM UPSTREAM CONVECTION
OVER THE NORTHERN PLAINS. OTHERWISE PARTLY SUNNY SKIES ARE EXPECTED
TODAY WITH HIGHS IN THE MID TO UPPER 80S.

LOW PRESSURE OVER IOWA WILL PUSH A WARM FRONT TOWARD LOWER MICHIGAN
TONIGHT AND SATURDAY. QUITE A BIT OF ELEVATED INSTABILITY WAS NOTED
ESPECIALLY AFTER MIDNIGHT TONIGHT INTO SATURDAY MORNING. LLJ POINTED
TOWARD SOUTH CENTRAL WISCONSIN WILL INTERSECT THE ADVANCING WARM
FRONT AND TSRA SHOULD DEVELOP OVER THE UPPER MISSISSIPPI VALLEY
TONIGHT AND THEN MOVE EAST. 0-6KM BULK SHEAR IS PROGD NEAR 50KTS
LATE
TONIGHT OVER THE WRN CWA. A BIG LIMITING FACTOR FOR TSRA DEVELOPMENT
THOUGH WILL BE THE PRESENCE OF A INVERSION NEAR 900MB. THIS CAP WILL
CREATE SOME RESISTANCE AND MAY PUSH THE SEVERE THREAT FARTHER SOUTH
OUT OF MICHIGAN.

PCPN CHANCES WILL DIMINISH SATURDAY INTO SATURDAY NIGHT AS THE LOW
PUSHES EAST THROUGH THE CWA. ANOTHER STRONGER LOW WILL APPROACH
SUNDAY. THIS LOW WILL BRING A STRONG SHORT WAVE WITH IT TOO. THIS
MAY BE OUR BEST CHANCE AT STRONG TO SEVERE STORMS ESPECIALLY SOUTH
OF I-96.  LI/S NEAR -6C COUPLED WITH MLCAPE AOA 2K J/KG AND LEFT
EXIT REGION UPPER JET DYNAMICS SHOULD RESULT IN STRONG STORMS.
HIGHER SHEAR VALUES NEAR 45 KTS ALONG/SOUTH OF I-94 SUGGEST A SEVERE
POTENTIAL TOO.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 328 AM EDT FRI JUL 25 2014

THERE IS A GOOD CHANCE OF SHOWERS AND THUNDERSTORMS SUNDAY NIGHT AS
THE SYSTEM OCCLUDES. ON MONDAY A PERIOD OF COOLER AND DRY WEATHER
FOLLOWS THE EXITING SYSTEM. AFTER THAT AFTERNOON AND EVENING SHOWERS
AND THUNDERSTORMS ARE POSSIBLE EACH DAY AS THE UPPER TROUGH REMAINS
IN PLACE LEAVING THE UPPER COLD POOL IN PLACE TOO. TEMPERATURES
SHOULD MODERATE TOWARD NORMAL BY THURSDAY.

THE MODELS REMAIN IN GOOD AGREEMENT ON THE OVERALL PATTEN FOR THIS
COMING WEEK. THAT IS AN UNSEASONABLY DEEP EASTERN TROUGH DEVELOPS BY
MONDAY AS THE PACIFIC SYSTEM PHASES WITH THE CANADIAN SYSTEM. THE
DEEP UPPER TROUGH THEN SLOWLY WEAKENS WITH TIME BUT SHORTWAVES
CONTINUE TO ROTATE AROUND THE SYSTEM MOST OF THIS COMING WEEK. THE
KEY TO ALL OF THIS THROUGH IS THE POLAR JET REMAINS SOUTH OF
MICHIGAN FROM MONDAY THROUGH THURSDAY. SO WITH THE  POLAR JET SOUTH
OF MICHIGAN AND THOSE SHORTWAVES ROTATING THROUGH EACH DAY THERE
REMAINS THE POTENTIAL FOR CONVECTION EACH DAY OF THE EXTENDED
FORECAST. THE SLOWLY INCREASING HEIGHTS AS THE SYSTEM WEAKENS WILL
ALLOW FOR A SLOW WARMING TREND TOO.

THE PHASING OF THE PACIFIC NORTHWEST SYSTEM WITH THE CANADIAN SYSTEM
SUNDAY INTO SUNDAY NIGHT HAS A SIGNIFICANT AMOUNT OF DYNAMICS
ASSOCIATED WITH IT. THERE IS EVEN SOME FGEN TO HELP THE CAUSE. THERE
IS ENOUGH INSTABILITY FOR THUNDERSTORMS SUNDAY NIGHT AS THE SYSTEM
OCCLUDES.  THE ECMWF SHOWS THE SHOWALTER INDEX BETWEEN -1 AND -2C
OVER MOST OF THE CWA AT MIDNIGHT AND THE TQ INDEX IS NEAR 20C (15C
IS THE THRESHOLD FOR THUNDERSTORMS).

MODEL SOUNDINGS FROM BOTH THE GFS AND ECMWF FROM THE 25TH/00Z RUN
BOTH SHOW VERY LITTLE IN THE WAY OF AN INVERSION OVER SOUTHWEST
LOWER MICHIGAN THROUGH MOST OF THIS COMING WEEK (TUESDAY >
THURSDAY). IN FACT EQUILIBRIUM LEVELS ON THE SOUNDINGS WED AND THU
ARE NEAR 35,000 FT. LITTLE QUESTION THAT WOULD YIELD THUNDERSTORMS.
MAYBE EVEN SOME SMALL HAIL. ON TUESDAY THE EQ IS AROUND 25,000 FT...
SO THE THREAT IS THERE FOR TUESDAY TOO.

THE BOTTOM LINE TO ALL THIS IS SHOWERY COOL WEATHER MOST OF THIS
COMING WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY)
ISSUED AT 1215 PM EDT FRI JUL 25 2014

VFR CONDITIONS WILL CONTINUE THIS AFTERNOON AND EVENING. SCATTERED
SHOWERS AND PERHAPS AN ISOLATED THUNDERSTORM WILL DEVELOP LATE THIS
EVENING AND OVERNIGHT. CONDITIONS WILL GRADUALLY DETERIORATE FROM
VFR TO MVFR DURING THE EARLY MORNING HOURS SATURDAY AS LOWER CLOUDS
AND STEADIER SHOWERS MOVE IN.

SHOWERS SHOULD GRADUALLY TAPER OFF DURING THE MID TO LATE MORNING
HOURS SATURDAY BUT CONDITIONS WILL LIKELY REMAIN MVFR THROUGH AT
LEAST MIDDAY SATURDAY DUE TO LOW CLOUDS.

&&

.MARINE...
ISSUED AT 328 AM EDT FRI JUL 25 2014

WIND AND WAVES WILL REMAIN BELOW ADVISORY CRITERIA TODAY.
HOWEVER...WINDS WILL INCREASE TONIGHT AHEAD OF LOW PRESSURE AND A
SCA/BEACH HAZARDS STATEMENT MAY BE NEEDED TONIGHT.


&&

.HYDROLOGY...
ISSUED AT 1206 AM EDT FRI JUL 25 2014

AFTER A STRETCH OF MAINLY DRY CONDITIONS FOR THE MAJORITY OF THE AREA
WE WILL SEE MULTIPLE CHANCES OF RAIN OVER THE NEXT SEVERAL DAYS.
ONE ROUND WILL DEVELOP AND MOVE THROUGH LATE TONIGHT AND INTO
SATURDAY MORNING WHILE THE ANOTHER ROUND WILL DEVELOP SUNDAY
AFTERNOON AND EVENING. AREA WIDE...TOTALS SHOULD AVERAGE OUT
AROUND ONE-QUARTER TO ONE-HALF INCH THROUGH SUNDAY. LOCALIZED HEAVIER
RAINFALL IS EXPECTED IN AND AROUND THUNDERSTORMS WHERE AMOUNTS ARE
LIKELY BE BE HIGHER.

ADDITIONAL CHANCES FOR RAIN EXIST GOING INTO NEXT WEEK. AT THIS
POINT LONG TERM 5-7 DAY TOTALS ARE MORE ON THE BENEFICIAL SIDE
WITH RECENT DRY WEATHER. OVERALL...RIVER FLOODING DOES NOT LOOK
LIKELY. ANTICIPATED RAINFALL SHOULD ONLY RESULT IN MINOR RISES.

&&

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

$$

SYNOPSIS...93
SHORT TERM...93
LONG TERM...WDM
AVIATION...LAURENS
HYDROLOGY...JAM
MARINE...93










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