Area Forecast Discussion
Issued by NWS Grand Rapids, MI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
436
FXUS63 KGRR 192344
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
744 PM EDT TUE JUL 19 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Tue Jul 19 2016

Hot and humid conditions will be overspreading the region through
the latter half of the week. Temperatures will be around 90, but
heat index values will climb toward 100 by Thursday. Widely
scattered storms will be possible in this muggy air mass, with the
best potential coming Thursday afternoon and evening.

The heat wave will continue into the weekend, with slightly cooler
weather by Monday and Tuesday. We will see continue to see a
chance of scattered storms, especially through Saturday night,
before we see drier air arrive.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 330 PM EDT Tue Jul 19 2016

A fair amount of changes to the forecast as the models are now
keeping the best jet dynamics to our north and west through much
of the short term. A cold front does approach the area by Thursday
and Thursday night which should give us the best chance for
showers/storms.

Convection still remains the big question mark to the short term,
but general trends is for much of it to stay to our NW. I`ve
lowered POPs for Wed and Wed night. The trend is for the storms to
remain out over MN and Lake Superior. The short wave that had been
shown to come through, now dampens out over the northern Lakes,
and there really is very little support for pcpn across SW MI.
Will keep 20/30 POPs going...mainly into Wed night...in case a few
of these showers and storms survive farther east, away from the
main dynamics.

A somewhat better Chance of storms should come into Thursday
afternoon and evening. Again jet dynamics are lacking over our
area, but with a cold front sagging SE into central Lower, there
will be the better chance that the storms survive being within the
better moisture pool along the front. Severe potential appears
very low throughout the short term.

As for the heat...we will see increasing humidity along with
hotter temps. Highs should reach the upper 80s to around 90 both
Wed and Thu, but with dew points reaching the 70s, heat index
readings will push toward 100 by Thu.

.LONG TERM...(Friday through Tuesday)
Issued at 330 PM EDT Tue Jul 19 2016

It would seem more likely than not that Friday will be the hottest
day of the year to date. That is with both the high and low
temperatures. Saturday will see continued hot weather but with a
greater chance of thunderstorms late in the day, highs may not be
quite as hot.  The passing of a cold front Saturday night will
bringing cooler air for the remainder of the period.

As we have been saying the upper high builds to nearly 600 dam,
centered over the Southern Plains into Friday.  The closed upper low
off the Pacific Northwest Coast is sheared out by the next upstream
shortwave in the Thursday time frame. That largely heads east
across the top of the central CONUS upper ridge but in doing so
deflates the upper ridge considerably allowing our Pacific Northwest
System to dig into the Northeast Conus late into the weekend and
early in the following week. That brings cooler northwest flow back
to Lower Michigan by Monday and that will continue into Tuesday.

The biggest question now is will there be enough convective clouds
around to mitigate how hot it can get Friday?  At this point it
seems the MCS will dive south across lower Michigan at during
Thursday night allowing for clearing by mid to late morning Friday.
That should allow Southwest Michigan to warm into the mid to upper
90s based on my 1000/925 mb Forest tool. This would result in a
heat index over 100 degrees.  This may mean we would need a heat
advisory for Friday but it is to early to pin that down.

I still think there should be enough convection around that most
places will see at least some rain before all of this is done by
Sunday afternoon.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 745 PM EDT Tue Jul 19 2016

Confidence is high that VFR weather will continue tonight and
Wednesday. An isolated shower or tstm cannot be completely ruled
out Wednesday afternoon, but the risk is too low to include in
the TAFs. Light and variable winds tonight will become south at 5
to 10 knots on Wednesday.

&&

.MARINE...
Issued at 330 PM EDT Tue Jul 19 2016

Long fetch southerly winds will create a choppy lake...mainly
north of Grand Haven by Wed afternoon. Little changes in this set
up until winds should drop off Thursday night as the front
approaches. For now this appears to be just under small craft
conditions.


&&

.HYDROLOGY...
Issued at 330 PM EDT Tue Jul 19 2016

With chances for thunderstorms the latter half of the week and into
the weekend, but low confidence in timing and coverage, the pattern
will likely continue to support many locations not getting enough
rain and some locations getting too much too quickly. WPC basin-
average QPF is advertising a range between a half inch to nearly 2
inches across the CWA through Friday evening, with greater amounts
favored toward the south and west. But as is typical with weakly
forced summer convection, rainfall totals will probably vary
substantially over short distances.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...WDM
AVIATION...Meade
HYDROLOGY...CAS
MARINE...JK



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.