Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/19/19
Area Forecast Discussion
National Weather Service Grand Rapids MI
845 PM EDT Thu Jul 18 2019
LATEST UPDATE...
Mesoscale Discussion
.MESOSCALE DISCUSSION...
Issued at 845 PM EDT Thu Jul 18 2019
Currently, a surface warm front is located from the Michigan/Indiana
border along Lake Michigan into south-central Wisconsin. South of
the front, dew points are in the upper 70s to even lower 80s, with
RAP-analyzed and 00Z RAOB confirmed MLCAPE >3500 J/kg and mid-
level lapse rates of 6.5-7 K/km. Bulk wind shear values along and
north of the front are 35-45 kts, with 0-1 km shear of 25-30 kts.
Implied isentropic ascent is increasing over Lower Michigan given
the recent increase in low- level clouds (e.g. warm air riding
over the cold dome of air from the storms this morning), with
convection already off and running across southern MN along the
nose of a developing low- level jet (35 kts sampled at 2 km via
DMX VWP). All in all, it appears the table is being set for
another active night across the Great Lakes.
As the LLJ strengthens after dark (progged 40-45 kts by 6Z/2AM)
and focuses into central Wisconsin, confidence is high that
convective coverage will increase considerably along a narrow axis
stretching into western Lower Michigan. Uncertainty however lies
in exactly where this zone will set-up (and if it will even
extends into Lower Michigan at all). CAMs favor the US-10
corridor, but visible satelite trends would suggest a smidge
further north. Then again, the zone may end up slightly further
south along the nose of the best low- level moisture which can be
seen via a narrow band of northeastward- moving clouds over Lake
Michigan as of this writing. Recent AMDAR soundings indicate
substantial capping centered at 850 mb coinciding with the zone of
maximum WAA basically from Chicago to Grand Rapids to Detroit, so
there may be a southern limit to how far anything can develop.
There is also uncertainty with when exactly convection will
develop, but confidence is high in the greatest coverage between
midnight and 8 AM.
With PWATS of 1.5-2" and westerly cloud-layer winds, the main
threat from thunderstorms tonight will be very heavy rain
especially as convective cores train over the same location.
However, considering the impressive instability and shear
(especially in the low-levels), a few storms may be capable of
producing hail to 1" in diameter. The tornado threat should be
curtailed by the elevated nature of the storms but anytime there`s
a low-level jet going right into a warm front, you can`t let your
guard down. Finally, it`s not out of question a localized wind
threat may materialize should cold pools consolidate and force a
compact line or two develop. All in all, we may be looking at a
multi-faceted nocturnal event mainly focused within a narrow zone.
&&
.SYNOPSIS...
Issued at 330 PM EDT Thu Jul 18 2019
- Heavy rain potential late tonight
- High humidity and heat through Saturday
- Much cooler and less humid next week
&&
.DISCUSSION...(This evening through next Thursday)
Issued at 330 PM EDT Thu Jul 18 2019
MCS finally moving out of the forecast area with clearing on the
back side which will allow temperatures to reach the 80s by
sundown across most places. We still should fall well short of
heat warning criteria, but the headline was left in effect given
the cumulative effect of a long period of 70 plus dew points.
Synoptic scale analysis shows upper ridge will remain anchored
south of Lower Michigan through Saturday and the big question mark
continues to be the extent of future MCS activity the next couple
days. Best guess is that we will see another area of convection
form across central Wisconsin overnight and track east into the
northern forecast area late tonight into Friday morning as shown
by most model guidance. This makes physical sense with expected
diurnal enhancement of low level jet in that area and with zonal
flow given the flat ridging. MBE vectors show potential for
backbuilding and training of storms which mean the flood potential
is high given PWATS over 2 inches and efficient warm rain
processes expected.
The MCS may turn southeast Friday morning as some expansion of the
cold pool is expected given thermodynamic processes as dry wedge
exists at mid-levels. This has the potential to again put a damper
on the high temperatures across the central and southern forecast
area on Friday afternoon.
Hot weather looks more likely Saturday across the southern half of
the forecast area as the upper ridge builds into this area and 850
and 925 mb temperatures peak. Then the cold front slides south
during the evening with strong storms and heavy rain potential.
Rain continues into Sunday as sfc wave moves through with much
cooler and drier weather next week under Canadian surface high
pressure.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 818 PM EDT Thu Jul 18 2019
VFR weather prevails across Southwest Lower Michigan at 800pm.
This will likely not remain the case tonight as we expect a round
of thunderstorms likely after midnight. Ceilings will remain VFR
outside of thunderstorms. Within storms however, there will be
brief times that ceilings and visibilities dip to IFR or
potentially lower as the rain cloud be heavy associated with them.
The most likely time frame for storms will be between midnight and
800am.
The area will likely be in a lull in the activity Friday morning
into the early afternoon hours. Another round of storms is
possible between 200pm and 800pm on Friday.
Bottom line is we will be VFR outside of storms, but a couple
rounds of storms the next 24 hours will be localized poor aviation
conditions.
&&
.MARINE...
Issued at 330 PM EDT Thu Jul 18 2019
Small Craft Advisory is unchanged. There could be areas of marine
fog Friday night and Saturday morning as winds decrease.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Excessive Heat Warning until 8 PM EDT Saturday for MIZ056>059-
064>067-071>074.
Beach Hazards Statement through Friday 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 Friday for LMZ846>849.
&&
$$
MESOSCALE...Borchardt
SYNOPSIS...Ostuno
DISCUSSION...Ostuno
AVIATION...Duke
MARINE...Ostuno