Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 250009
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
809 PM EDT SUN AUG 24 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 328 PM EDT SUN AUG 24 2014

MONDAY AND TUESDAY WILL SEE WARMER AND MORE HUMID CONDITIONS WITH
SCATTERED THUNDERSTORMS. SOME HEAVIER RAIN IS POSSIBLE TUESDAY
NIGHT AS A COLD FRONT SINKS SOUTH THROUGH LOWER MICHIGAN.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 328 PM EDT SUN AUG 24 2014

FORECAST IMPACTS IN THE NEAR TERM INCLUDE PATCHY FOG TONIGHT ALONG
WITH HEAT INDICES IN THE LOWER 90S MONDAY AND TUESDAY AFTERNOON.
SCATTERED THUNDERSTORMS ARE POSSIBLE AS LIFTED INDICES ARE AROUND
MINUS 6 BOTH DAYS...BUT COVERAGE WILL BE ISOLATED TO SCATTERED
BEFORE THE COLD FRONT ARRIVES LATER TUESDAY TO FOCUS CONVECTION.
SEVERE WEATHER RISK IS LIMITED AS SHEAR REMAINS RELATIVELY WEAK.
FLOODING POTENTIAL IS THERE HOWEVER. SEE HYDROLOGY SECTION FOR
DETAILS. LOOKS LIKE THE MOST FAVORABLE CONDITIONS FOR HEAVY RAIN
OCCUR TUESDAY NIGHT.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 328 PM EDT SUN AUG 24 2014

A COLD FRONT SHOULD BE NEAR THE MI/IN BORDER WEDNESDAY AS HIGH
PRESSURE BUILDS IN FROM WISCONSIN. WE PUSHED POPS A BIT FARTHER
SOUTH WEDNESDAY BUT THE EXACT POSITION OF THE FRONTAL BOUNDARY ISN/T
CERTAIN AT THIS POINT. IT/S LIKELY THOUGH THE THE BULK OF THE PCPN
ASSOCIATED WITH THE BOUNDARY WILL BE OVER NORTHERN INDIANA OR
PERHAPS FAR SOUTHERN LOWER MICHIGAN.

THE BOUNDARY BEGINS LIFTING NORTHWARD THURSDAY IN RESPONSE TO
DEVELOPING LOW PRESSURE IN THE PLAINS. WE/LL KEEP A SLIGHT CHANCE OF
PCPN IN THE GRIDS BUT MOST LOCATIONS WILL BE DRY.

THE BEST CHANCE OF RAIN LOOKS TO BE FRIDAY/SATURDAY WHEN THE LOW
MOVES ENE TOWARD LOWER MICHIGAN AND THE WARM FRONT MOVES NORTH
ACROSS THE CWA. HIGHS WILL BE IN THE MID TO UPPER 70S THROUGH THE
PERIOD.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED A 808 PM EDT SUN AUG 24 2014

CURRENTLY VFR CONDITIONS PREVAIL ACROSS ALL OF OUR TAF SITES. I
WOULD EXPECT WE WOULD CONTINUE TO SEE VFR CONDITIONS UNTIL BETWEEN
04Z AND 06Z WHEN SOME LIGHT FOG SHOULD START TO DEVELOP AS IT HAS
THE PAST 3 NIGHTS. TONIGHT... UNLIKE THE LAST FEW NIGHTS THERE
WILL BE LESS CLOUD COVER AROUND BY 03Z OR SO. I WOULD THINK SKIES
WOULD BE NEARLY CLEAR. THAT WOULD HELP FOG TO DEVELOP. WHAT IS NOT
SO SUPPORTIVE OF FOG THROUGH IS THE 15 TO 25 KNOTS OF WIND IN THE
BOUNDARY LAYER AT MOST OF THE TAF SITES TONIGHT IN THE 03Z TO 09Z
TIME FRAME. ANOTHER ASPECT TO THIS IS THE MOISTURE FEED FROM LAKE
HURON AND LAKE ERIE DOES NOT COME INTO PLAY AT ANY OF THE TAF
SITES SINCE SURFACE WINDS WILL BE MORE SOUTH SOUTHEAST. SO I DID
NOT PUT DENSE FOG IN ANY OF THE TAF SITES.

THE OTHER FEATURE TO WATCH IS TOWARD MORNING THE CONVECTION
ALREADY DEVELOPING OVER MINNESOTA WILL BE DEVELOPING TOWARD
SOUTHWEST LOWER MICHIGAN IN THE 10Z TO 12Z TIME FRAME. MODEL
SOUNDINGS SHOW AS MUCH AS 2000 J/KG OF ELEVATED CAPE NEAR US-31 IN
THE 12Z TIME FRAME AS THIS CONVECTION MOVES IN. SO IT IS MORE THAN
POSSIBLE THAT MKG SHOULD SEE SHOWERS/THUNDERSTORMS BETWEEN 11Z AND
14Z. TO A LESS EXTENT GRR...AZO AND BTL MAY ALSO SEE SOME OF THIS
AS THE STORMS MOVE INLAND AND DISSIPATE. I PUT VCSH / VCTS IN THE
MORE WESTERN TAF SITES TO COVER THIS POSSIBILITY.

AFTER THIS MOVES THROUGH THERE IS TO MUCH DRY AIR TO MUCH MORE
THAN SOME SHALLOW CU. SO VFR CONDITIONS SHOULD PREVAIL THROUGH THE
AFTERNOON AT ALL TAF SITES.

&&

.MARINE...
ISSUED AT 328 PM EDT SUN AUG 24 2014

WINDS WILL VEER TO THE SOUTH ON MONDAY BUT WAVES WILL ONLY BUILD
TO AROUND 2 FEET AS FLOW WILL BE RELATIVELY LIGHT. VISIBILITY COULD
BE REDUCED AT TIMES IN FOG TONIGHT THROUGH TUESDAY. THUNDERSTORMS
ARE POSSIBLE MONDAY AND TUESDAY AFTERNOONS.


&&

.HYDROLOGY...
ISSUED AT 1104 AM EDT SUN AUG 24 2014

BEST CHANCE FOR SIGNIFICANT RAINFALL WOULD BE MONDAY NIGHT THROUGH
WEDNESDAY WITH A SLOW MOVING COLD FRONT. THIS IS NOT A GUARANTEE
AS THE LLJ IS FORECAST TO BE QUITE WEAK. NEVERTHELESS...A VERY
MOIST ATMOSPHERE COMBINED WITH FORCING VIA THE COLD FRONT AND SLOW
CELL MOVEMENT COULD RESULT IN SOME SIGNIFICANT RAINFALL IF STORMS
DEVELOP OVER OUR AREA. PW VALUES WILL LIKELY BE AROUND 1.75"
MONDAY NIGHT AND TUESDAY. MODEL GUIDANCE IS MIXED REGARDING HOW
LONG THE FRONT MAY HANG UP...SO IT IS UNCLEAR WHEN THE THREAT FOR
SIGNIFICANT RAINFALL WOULD END.

&&

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

$$

SYNOPSIS...OSTUNO
SHORT TERM...OSTUNO
LONG TERM...93
AVIATION...WDM
HYDROLOGY...HOVING
MARINE...OSTUNO






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