Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 242217
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
617 PM EDT SUN JUL 24 2016

LATEST UPDATE...
Mesoscale Discussion

.MESOSCALE DISCUSSION...
Issued at 615 PM EDT Sun Jul 24 2016

The airmass seems to have recovered from earlier convection with
current, 22Z, temperatures in the upper 80s and dew points in the
mid to upper 70s. LAPS soundings show very unstable atmosphere
across much of the forecast area with sfc based Lifted Indices of
minus 8, CAPEs over 3500 J/Kg and little or no convective
inhibition. Deep layer shear is weak, however, at around 15 to 25
knots and there is little in the way of discernible boundaries to
focus updrafts.

Storms currently over Lake Michigan appear to be sfc based and
have shown a general weakening trend after moving over water.
With the weak shear profiles we expect any storms that form across
the forecast area this evening to be more of the pulse type with
potential for wet microbursts given the dry wedge at mid levels
seen in LAPS soundings. Given high sfc based instability, multicell
clusters of storms may form on the outflow of collapsing updrafts.

&&

.SYNOPSIS...
Issued at 330 PM EDT Sun Jul 24 2016

A cold front will bring scattered showers and thunderstorms
this evening. High pressure will build in and produce fair and
continued very warm weather Monday through Tuesday. Temperatures
should cool slightly to near normal late in the week into next
weekend.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 330 PM EDT Sun Jul 24 2016

Primary short term fcst concerns involve assessment of convective
potential late this afternoon and evening.

Scattered showers will linger mid to late this afternoon and a few
thunderstorms should redevelop late this afternoon and evening
along and out ahead of the approaching cold front. Convective
potential is mitigated by several factors including weak lift from
the front. Upper level dynamics/pva favorable for convective
development will stay well north of our area.

Nevertheless we do expect scattered thunderstorms to redevelop
late this afternoon and evening in the axis of weak sfc convergence
near the approaching front. Vis sat trends show a cu field developing
near MKE ssw to near Rockford with a developing line of showers and
thunderstorms.

We cannot rule out potential for strong to marginally severe storms
late this afternoon and evening with hail and gusty winds. This is
largely contingent on extent of mid to late afternoon
diurnal heating. 19Z mesoscale analysis does show moderate
instability building into our far sw fcst area south of KGRR out
ahead of the developing line of convection over extreme SE
WI/northern IL.

The relatively best chance for organized convection and severe
weather will stay a little further south of our area across portions
of IL/IN late this afternoon and evening where 19Z mesoscale analysis
indicates much stronger instability. Convection will develop
there on outflow boundaries from the MCS earlier today and also along
and just ahead of the cold front.

Fair weather will return Monday through Tuesday as high pressure
builds in behind the departing system. It will remain very warm
with high temps in the mid to upper 80s both days but there will
be somewhat less humidity.

.LONG TERM...(Wednesday through Sunday)
Issued at 330 PM EDT Sun Jul 24 2016

Surface high pressure that is in place at the beginning of the
period will begin to break down and move eastward by Wednesday
afternoon. Medium range models continue to point to more of a zonal
flow pattern during the midweek period with increasing chances for
showers and thunderstorms during the later half of the work week.

Upper level ridging that was responsible for bringing low to mid-90s
to the area will continue to weaken, eventually being outdone by
a building high over the Southwestern U.S. by Thursday. This results
is somewhat of northwest tilt to the 500mb heights over the Upper
Midwest, which coincides with a broad trough. A weak surface low
takes shape over Southeastern Iowa, slowly tracking into the Southern
Great Lakes through the end of the week.

It does not look like a wash out by any means, but each day could
feature at least the chance for a few showers and thunderstorms. The
likelihood is that the best rain probabilities hold off until late
Thursday into Friday as the main area of lift pushes northeast
through Lower Michigan. Temperatures look much more comfortable with
highs hovering closer to average, even slightly below normal by
Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 156 PM EDT Sun Jul 24 2016

Early morning convection has progressed into Southern Lower
Michigan and weakened. A broken liNe of storms stretches across
Central Lower Michigan and may become the focus for additional
develop this afternoon.

The level of instability is in question with early morning rainfall
and leftover cloud cover. Therefore, VCTS has remained in the TAFS
for all sites this afternoon with occasional gusts near 20kts
possible. CIGS and VSBYS should remain in VFR territory for a
large portion of the time with exception to any thunderstorm
affected sites. This will have to be adjusted accordingly if
thunderstorm development becomes more widespread.

Once the front moves through the main concern tonight is the
potential for fog. I remained optimistic with most locations
staying MVFR. Southern sites seem to have the best potential to
dip into IFR momentarily before sunrise. Conditions should quickly
improve going into Monday with lifting CIGS and clearing skies.


&&

.MARINE...
Issued at 330 PM EDT Sun Jul 24 2016

A small craft advisory and beach hazards statement remains in
effect through late this afternoon from Grand Haven north to
Manistee due to brisk south southwest winds up to 20 to 25 kts
resulting in waves up to 4 to 5 feet. Scattered thunderstorms
could also pose a hazard to mariners through mid evening. Fair
weather with fairly minimal winds and waves returns Monday through
Tuesday.


&&

.HYDROLOGY...
Issued at 1250 PM EDT Sun Jul 24 2016

No river flooding is expected through next week. Area wide rain of
around an inch with locally up to 3 inches (mainly near Lake
Michigan) has fallen since Saturday evening. Another wave of showers
and storms are possible tonight. A small chance of rain is also in
the forecast Wednesday through Friday. River levels are at or below
normal for this time of year, so this rain should not bring any
rivers to flood.

Strong thunderstorms could produce localized rainfall totals over an
inch and lead to localized ponding of water. Rainfall totals will
probably vary substantially over short distances.

&&

.GRR Watches/Warnings/Advisories...
MI...Beach Hazards Statement until midnight EDT tonight for MIZ037-
     043-050.

LM...Small Craft Advisory until midnight EDT tonight for LMZ847>849.

&&

$$

MESOSCALE...Ostuno
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...JAM
AVIATION...JAM
HYDROLOGY...63
MARINE...Laurens



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