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Area forecast discussion
National Weather Service Grand Rapids Michigan
328 am EDT Fri Jul 19 2019

Latest update...
synopsis/discussion/marine

Synopsis...
issued at 330 am EDT Fri Jul 19 2019

-showers and thunderstorms this morning; locally heavy rainfall
possible

-excessive heat this afternoon into Saturday

-additional showers and storms from late Saturday into Sunday

-lengthy stretch of dry and cooler/less humid weather next week

&&

Discussion...(today through next thursday)
issued at 330 am EDT Fri Jul 19 2019

No changes to heat headlines as sfc dew points have risen into the
mid to upper 70s and sunshine is expected to emerge this
afternoon behind morning mesoscale convective system. Still forecasting highs 90-95 today
with heat indices 105-110 south of I-96 and around 100 to the
north. Similar conditions Saturday before fropa Saturday night.

Scattered convection has been struggling to develop overhead early
this morning, probably due to the very warm air aloft. (Latest
rap shows 700 mb temps around 13.5c.) However a mature mesoscale convective system is
currently upstream over srn WI and this convection should continue
east-southeast along the cape gradient this morning toward SW Michigan.

Some uncertainty exists as to the strength of the convection and
wind gust potential as mesoscale convective system arrives from the west, especially since
the low level jet feeding into it is shown to diminish
considerably by 12z. Heavy rainfall is main concern this morning
due to pwats around 2 inches and 800 mb dew pts near 20c.

Strongest convection currently near Madison WI (containing
intense lightning) looks to hit the Lakeshore south of Holland or
South Haven around 12z/8 am EDT based on it's currently
trajectory. However that said, the coldest cloud tops in infrared appear
to be backbuilding and that eastern-most convection near Madison
may weaken over the next few hours in favor of convection farther
west/northwest.

After morning convection weakens due to the waning llj, will have
to watch for the potential of re-newed diurnal development on
leftover outflow boundary and/or mesoscale convective vortex from the Wisconsin nocturnal
mesoscale convective system. Latest infrared suggests there are even some Gravity waves
spreading eastward from that mesoscale convective system. Latest cams suggest that renewed
development this afternoon will occur in a band from fnt to azo,
although the warm temps aloft may keep things capped in SW mi,
with most activity being to our east near Detroit/lk Erie.

Mixed signals for tonight with cams suggesting a Bow echo racing
across nrn WI this evening then curving southeast across the area north
of I-96. This seems unreasonable though since heights will be
rising tonight and 700 mb temps soar to warmer than 14c over the
entire area. Values this warm would almost undoubtedly keep things
capped and dry tonight. Therefore believe (despite extreme
instability with CAPES near 5000 j/kg) that nocturnal mesoscale convective system activity
will stay mostly north of our area tonight and if something does
make a run at US from nrn WI, it should weaken as it does so.
Worst case scenario would likely be residual gusty outflow winds
near Ludington/U.S. 10 vicinity.

Chances for showers and tstms increase across nrn areas by
Saturday afternoon, then across the entire area on Saturday night
as the sfc front sinks south and mid level cap erodes. Sfc front
settles south of the area on Sunday, but wave moving along the
front keeps rain potential alive for srn sections. Most of next
week looks dry and much less humid with high pressure dominating.



&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 1242 am EDT Fri Jul 19 2019

Primarily VFR conditions are anticipated at all the terminals
through the next 24 hours. However development of scattered
showers and thunderstorms during the early to mid morning hours
today could cause brief reductions to MVFR or IFR which could
linger into late morning before tapering off. Most of the rest of
the day Friday afternoon into Friday evening should be dry with
VFR conditions.



&&

Marine...
issued at 330 am EDT Fri Jul 19 2019

Small Craft Advisory/beach hazards conditions look marginal today
since the low level jet is shown to diminish. That said, a wake
low developed behind the departing convection yesterday morning
and produce some strong wind gusts in excess of 40 kts. Confidence
in that occurring again is low, but will keep all marine
headlines intact for now.

&&

GRR watches/warnings/advisories...
Michigan...excessive heat warning until 8 PM EDT Saturday for miz056>059-
064>067-071>074.

Beach hazards statement through this evening for miz037-043-050-
056.

Heat advisory until 8 PM EDT Saturday for miz037>040-043>046-
050>052.

Lm...Small Craft Advisory until 8 PM EDT this evening for lmz846>849.

&&

$$

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