Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1158 PM EDT Friday may 29 2015
Showers and isolated thunderstorms will have greatest coverage in
the mbs to fnt terminal areas during the remainder of the night.
This area will also see the first signs of the cold front during
Saturday morning when showers will become more widespread.
Thunderstorms will remain limited until daytime heating increases by
afternoon along and south of the front. This favors locations from
fnt southward through the dtw corridor as having the best chance of
storms through Saturday evening. IFR ceiling and a sharp wind shift
to the northeast is expected behind the front lasting through
For dtw... the band of showers moving through central lower Michigan
shortly after midnight will brush through dtw during the early
morning. Conditions will then be on the quiet side until coverage of
showers and storms ramps up during the afternoon and peaks with the
frontal passage. The northeast wind shift looks solid at 22z with
IFR ceiling lasting through Saturday night Post frontal passage.
//Dtw threshold probabilities...
* medium for ceiling 5000 feet or less during the afternoon...high
* Low for thunderstorms tonight...medium during the
Previous discussion...issued 1032 PM EDT Friday may 29 2015
The Tri Cities...northern thumb...down to about the Interstate 69
corridor will be the area remaining most active in terms of
showers and thunderstorm overnight through Saturday morning. The
next cluster of activity is on the way through central lower at
press time. Hourly mesoanalysis indicates MLCAPE still hanging in
the 500 to 1000 j/kg range so expect isolated thunderstorm
coverage to continue for a few more hours before trending toward
just increasing coverage of showers as the cold front approaches.
Model depictions indicate 850 mb Li rising above zero overnight as
an indication that elevated instability will diminish enough for
no more than a rumble of thunder until late morning. That being
said...the front will be strong enough to get storms going again
relatively early in the diurnal cycle Saturday afternoon. Rainfall
probability in the likely to categorical range looks solid
throughout the day.
Previous discussion...issued 413 PM EDT Friday may 29 2015
Short term...through tonight
Coverage of rain this morning into the early afternoon over extreme
southeastern parts of the County Warning Area was able to be maintained as they
moved along the Theta-E ridge and good low level lapse rates. These
showers will exit the area over the next hour or so. Clouds have
been rather persistent today and are now just starting to thin
somewhat...however this will be short lived as more clouds move in
later this evening. Temperatures have warmed nicely across the County Warning Area despite
cloud cover given the decent southerly flow into the area. The rest
of the afternoon should remain dry over most of the area with the
chances for more precipitation increase again tonight. Latest radar shows
development back across southwestern lower and northern Indiana with
uptick in activity driven by diurnal heating. This activity
however is expected to diminish going through the evening with loss
of heating. Much of the County Warning Area will not see a whole lot of activity
with the exception of the northwestern County Warning Area...Tri-Cities area...as
showers and isolated thunderstorms are possible given the better
instability and lapse rates across northern lower Michigan with no
severe weather expected tonight. Slight chance probability of precipitation have however
been maintained in the grids across the eastern two thirds of the
area going into the overnight hours as precipitable water values remain above 1
inch. Given the area will continue to reside in a warm moist
airmass...expect temperatures tonight to stay on the warm side with lows
only dropping down to the upper 60s.
Long term...Saturday through Friday
Low confidence forecast remains with regard to timing/strength of
thunderstorms Saturday with this forecast cycle. Probably for rain
remains high however. There is also some uncertainty now with timing
the exit of the cold front and precipitation along it...which bleeds
some uncertainty into Sunday as well now.
Upper low over northern Manitoba will slide through Ontario and into
Quebec by Saturday night. Baggy upper trough over the central Continental U.S.
Will phase with this feature as it moves east. Result will be a
surface trough and cold front that extends from the upper Great
Lakes down to the Gulf Coast by tomorrow. Smaller upper waves
lifting up ahead of the main system...and ahead of the cold
front...will help generate rounds of convection along/ahead of the
front. These waves are harder to time in general because of their
smaller scale...especially when some are generated/affected by
upstream convection. Models are struggling to resolve how these
waves will affect the timing of the cold front through Southeast
Michigan...with the main source of uncertainty centered around the
strong upper wave seen on water vapor over eastern Texas. GFS/NAM
remain more in line with the idea that it will be shunted south by
the approaching trough to our west...while the Gem and especially
the new 12z Euro allow it to slip up closer to or even into Michigan
by Saturday night. This second scenario would delay the passage of
the front...keeping it positioned over the southern Great Lakes
longer and keeping rainfall and possible thunderstorms going
overnight and even into Sunday.
Otherwise...initial set-up looks the same to start Saturday. Strong
southwest flow will continue to usher in moisture...with precipitable water values
rising just above 1.75 inches in the warm sector ahead of the front.
What remains of convection currently aligned along the front
stretching from northern Michigan down through Oklahoma should work
into the northwest portion of the forecast area Saturday
morning...then slowly drop south with the front. This activity
should then continue to slide south through the day and evening.
Expectation is that fgen and right entrance region forcing will help
provide a more solid area of lift by late afternoon and
evening...leading to the development of a broader area of
precipitation. Thunder may be embedded within this area...but there
also potential for thunderstorms...potentially strong from M-59
south...to develop ahead of the front earlier in the day.
Frontal passage is still forecast for late Saturday
afternoon/evening...but will need to watch potential for upper
portions of the front to become stalled over the area into Sunday.
Behind the front...cool and dry conditions will build in for the
remainder of Sunday and Sunday night.
Global models in good agreement on a quiet stretch of weather from
Monday into at least the middle of next week. Secondary shortwave
passing across northern Michigan Monday will reinforce the longwave trough
over the Great Lakes leading to another cooler-than-normal day but
given the lack of moisture a dry day is anticipated. Heights
gradually rise Tuesday through Thursday leading to a nice warming
trend. Sprawling surface anticyclone and dry airmass should result
in a dry forecast through at least Wednesday. Return flow looks to
set up Thursday Friday with warmer and more humid conditions
returning. Given lack of forcing signal will keep the forecast dry
through Friday for now.
The chance for showers and thunderstorms will increase tonight and
on Saturday as a strong cold front is driven into the Great Lakes
region. This front is forecast to track across Lake Huron late
tonight and early Saturday before reaching Lake Erie Saturday
evening. Winds will remain southerly through this evening before
they start to flip to the northwest behind the cold front as it
works south through the second half of the night and tomorrow. Winds
will also increase in speed behind the front as colder air rushes in
and increases instability in the lower-levels of the atmosphere. The
strongest period of winds looks to occur over the southern portion
of Lake Huron...Lake St Clair...and Lake Erie Saturday night into
Sunday behind the cold front and before high pressure builds into
the area. Small craft advisories may be required...especially as
winds turn northeast and allow higher waves to build over Southern
Lake Huron. Winds and waves will weaken late Sunday into Monday as
high pressure builds in from the northern Great Lakes.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
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