Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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273
FXUS63 KGRR 211934
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
334 PM EDT THU JUL 21 2016

LATEST UPDATE...
Synopsis/Short Term/Long Term/Hydro/Marine

.SYNOPSIS...
Issued at 334 PM EDT Thu Jul 21 2016

A weak cold front will move slowly south tonight triggering
additional thunderstorms. Locally heavy rain is possible from
these storms. The cold front will continue to slip southward into
Saturday so lingering thunderstorms are possible south of I-94
Friday morning. Otherwise hot and humid conditions are expected
Friday and Saturday as this is a really weak cold front. A much
stronger cold front will move across the area Sunday. that will
trigger additional storms. Temperatures will be close to normal
early next week behind the cold front that comes through Sunday.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 334 PM EDT Thu Jul 21 2016

The main issue tonight will be the treat of additional
thunderstorms. the heat advisory will be continued for Friday.
It may be needed Saturday but I am not sure enough of that to
extend it at this time.

The current area of thunderstorms should be totally out of our CWA
by 4 pm. then the question becomes can storms redevelops? There
is a cold front dropping south into our forecast area tonight and
it will only slowly move south through the CWA, not clearing the
southern CWA till Friday afternoon. So the low level jet may help
redevelop storms this evening that will sink south overnight.

Once those storms clear the area by mid morning Friday. The I
expect hot and humid conditions to prevail through Saturday
night. the next cold front may trigger more storms Saturday night.

Assuming the morning convection does clear the area Friday, I
would expect highs in the mid 90s. Combine that with dew points
near 70 and heat index values should reach around 100. This may
happen Saturday but my confidence in that is to low to extend the
headline at this time.




.LONG TERM...(Sunday through Thursday)
Issued at 334 PM EDT Thu Jul 21 2016

Main weather in the long term comes in the first period or two,
Sunday and Sunday night. A shortwave trough will be traversing the
northern Great Lakes and Ontario which will swing a cold front
through the area. The ECMWF is indicating a 30-35 knot LLJ over the
CWA Sunday afternoon and evening. CAPE values via the ECMWF are on
the order of 2000-3000 J/KG. Deep layer shear is 30-40 knots across
Central Lower, so a severe threat will need to be watched going
forward.

Still warm and humid heading into Sunday, with some relief coming in
the wake of the cold front. Highs Monday through Wednesday will be
more typical in the lower to middle 80s in most areas. Dry weather
is forecast Monday through Wednesday with a high shifting east
through the area. Another shortwave in zonal flow will bring
additional chances for showers and storms in the Wednesday night
and Thursday time frame.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 153 PM EDT Thu Jul 21 2016

Line of thunderstorms moving through the area will continue off to
the east and southeast through 21z. As the line moves through each
TAF site, expect west winds gusting to 30-35 knots and heavy rain.
It is possible that the line will increase in intensity and gusts
could potentially go higher than 35 knots. 1-2 hour period of MVFR
and IFR conditions are expected as the line is moving through, but
we should pop back up to VFR later this afternoon.

Tonight, we may see another round of storms from 03z-10z moving
from north to south through the area. Confidence in this at this
time is not high and have VCSH in the TAFs for now. Included some
light fog tonight in a post rain, very humid airmass. Conditions
should improve to VFR once again Friday morning after about 14z.


&&

.MARINE...
Issued at 334 PM EDT Thu Jul 21 2016

I will continue the beach hazard and Small Craft Advisories into
this evening then let them expire this evening. The core of the
strongest winds will come through between now and 8 pm this
evening. Beyond that I see no big issues for our Near Shore.

&&

.HYDROLOGY...
Issued at 334 PM EDT Thu Jul 21 2016

Rainfall is not expected to be heavy enough to result in large
scale flooding of rivers or streams in the coming week. Even so,
locally heavy rain from thunderstorms tonight may cause some
localized flooding in areas with poor drainage and flashy streams.

&&

.GRR Watches/Warnings/Advisories...
MI...Heat Advisory until 7 PM EDT Friday for MIZ044>046-050>052-
     056>059-064>067-071>074.

     Beach Hazards Statement until 5 PM EDT this afternoon for MIZ037-
     043.

LM...Small Craft Advisory until 8 PM EDT this evening for LMZ848-849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...Duke
AVIATION...Duke
HYDROLOGY...WDM
MARINE...WDM



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