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fxus63 kgrr 200952 

Area forecast discussion
National Weather Service Grand Rapids Michigan
552 am EDT Tue Aug 20 2019

Latest update...

issued at 300 am EDT Tue Aug 20 2019

- chance of storms today through Wednesday

- dry weather Wednesday night through the weekend into next week

- cooler temps late in the week into the weekend


issued at 542 am EDT Tue Aug 20 2019

The pops were updated this morning to account for the storms
moving onshore in Allegan County. They will likely continue
east...staying between i96 and i94. These storms were forming
along and elevated warm front that does not move much over the
next few hours.


Short term...(today through thursday)
issued at 300 am EDT Tue Aug 20 2019

The primary fcst challenge is to assess convective potential for
today through Wednesday.

A consensus of latest cams and href members suggests that an mesoscale convective system
will develop over Iowa early this morning and become well
organized/forward propagating as it moves ESE across Illinois later
this morning and in later this aftn. So most of the organized
convection will stay south to SW of our fcst area later today.

However it is noted that a consensus of latest href members
suggests that fairly strong instability will develop over our
southern fcst area late this morning and aftn (ensemble mean sb
cape values reaching 2-3k j/kg). Fortunately deep layer shear
later today is rather weak and there is a lack of a stronger
forcing mechanism for convective initiation to occur.

Nevertheless isolated strong to marginally severe storms seem
possible given strong instability and rather dry air aloft and
steep mid level lapse rates. Some guidance fcst soundings suggest
dcape values may reach around 1k j/kg this aftn too so isolated
damaging wind gusts also seem possible in addition to hail. A
shortwave moving in from the NW and possibly an MCV will be the
forcing mechanisms for sct convective development later today.
Convective potential will increase if an MCV over Iowa moves further
north than currently expected.

Just a smaller chance for showers and storms will linger tonight.
Then on Wednesday some stronger convection could potentially
develop over our se fcst along and just ahead of the cold front.
The latest European model (ecmwf) is concerning as it suggests sb cape values could
reach around 3k j/kg toward kjxn late Wed am/early Wed aftn along
and just ahead of the cold front. Dry wx is fcst Wednesday night
through the weekend into early next week.

Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 1140 PM EDT Mon Aug 19 2019

Patchy fog will develop overnight and cause conditions to
gradually deteriorate to MVFR with some IFR possible mainly at our
southern terminals during the early morning hours Tuesday.
Conditions will improve to VFR at all the terminals during the mid
morning hours.

VFR conditions will continue in the afternoon and scattered
showers will develop. A few thunderstorms may develop as well
Tuesday afternoon with the relatively best chance for a storm at
our southern terminals from mid afternoon to early Tuesday
evening. Storms and heavier showers could cause brief reductions
to MVFR/IFR conditions.

issued at 300 am EDT Tue Aug 20 2019

Rather minimal wind speeds and wave heights are fcst today through
tonight. Winds will veer to the SW and increase a bit to around
10 to 15 kts this aftn.

Winds will veer to the NW and increase to around 15 to 25 kts
Wednesday after cold frontal passage and cause wave heights to
build to around 3 to 5 feet. A Small Craft Advisory could be
needed for Wed aftn/eve.

GRR watches/warnings/advisories...


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