Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
310 PM EDT sun may 24 2015
Short term...this afternoon and tonight
Rain showers will become more numerous over the Saginaw Valley late
today into this evening as low pressure lifts north through the middle
Mississippi Valley and a warm front extending east from this low
becomes better defined with time. With persistent lift and moisture
pooling with this features...dry low levels at or below 8kft will eventually
saturate with the widespread virga of today reaching the surface
before the front shifts north overnight.
The chance for measurable rain will also increase slightly south
into the I-69/M-59 corridor...but remain relatively low during the
same time frame late this afternoon and early this evening. In
general...really only expect scattered sprinkles south of I-69 as
both dry air and extra capping from upper level ridge continue to
inhibit shower coverage/intensity. When all is said and down...do
expect likely to categorical probability of precipitation over the Saginaw Valley...with a
tight gradient southward...tapering to little/no chance of
measurable rainfall from around I-94 or so south to the Michigan
and Ohio state line.
Very mild temperatures in the 70s to around 80 will only edge back
into the lower to middle 60s overnight as warm sector south of the warm
front expands north through the area and dew points steadily rise
this evening into tonight.
Shortwaves will continue to eject across the middle MS valley and
across the western Great Lakes as deep layer SW flow persists around
large scale anticyclone over the East Coast and mean troughing in
Next two shortwaves to impact the area are evident on WV imagery
over central Texas and southwest New Mexico. The former will lift
north within prevailing SW flow tonight, bringing with it the
remnants of this afternoon's arklatex region convection. Without
respectable large scale support, remnants will struggle to penetrate
the dome of dry air over Southeast Michigan. This is well-depicted
by the 12z WRF-arw/nmm and 4km NAM. Given the rather nebulous
forcing situation as the primary shortwave dynamics remain displaced
to the west, preferred to move forward with a conservative forecast.
It appears that the best chance for showers or thunderstorms will be
during a brief window 19-21z when the 700 mb-500 mb moisture axis swings
through the County Warning Area during peak heating. A partial coverage of showers
does appear likely, but expectation for lower coverage precludes a
higher pop mention. Lapse rates will be meager at best, so cape of
perhaps 400-500 j/kg will be spread thin and thunder will hard to
come by, much less any kind of severe threat. Most noteworthy
sensible weather feature for Monday will be dewpoints rising well into
the 60s and winds gusting to 25 knots as the boundary layer grows to
900mb per 4km NAM and mixes down stronger winds aloft.
Continued southwest flow will sustain warm and muggy conditions
Monday night as the second shortwave supports another convective
episode over the arklatex. This wave will lift north in similar
fashion, and is depicted to be only slightly stronger than its
predecessor. There may be a window for a higher probability of
showers by Wednesday night as this wave actually turns the mean flow
cyclonic for a brief time, but it's hard to argue for anything
higher than a 40 pop at this time.
A fairly active pattern remains for the extended period as a
series of low pressure systems are forecasted to impact Southeast
Michigan. Rain and thunderstorm chances will begin Wednesday
morning. The only dry day could be on Thursday when high pressure
tries to nudge its way into Southeast Michigan. Rain showers return
on Friday and Saturday. Have only included chance probability of precipitation into the
forecast for now to account for uncertainty in the timing of these
systems. High temperatures will remain in the upper 70s to low 80s
through Thursday with Friday highs approaching the middle 80s in some
Small craft advisories are in effect for all nearshore waters and
Lake Saint Clair for Memorial Day. Southwest wind will become
moderate to fresh over all area waters by late in the morning. Wind
gusts are forecast to frequently reach 22 to 26 knots. Offshore
winds will limit the potential for wave growth in the nearshore
zones with significant wave heights expected to maximum out around 2 to
locally 3 feet. Maximum wave heights will reach 4 to possibly 5
feet...mainly further away from shore. Thunderstorm potential is low
with only a slight chance during the afternoon.
Aviation...issued 1250 PM EDT sun may 24 2015
While rain showers and isolated thunder will be possible on lead edge of
encroaching Theta-E ridge...very dry low levels at or below 10kft will keep
most activity virga today/this evening. Upper level ridge will also
impede most convective development from kfnt/kptk southward. Will
maintain a window for rain showers at kmbs this evening...but lift this
north of terminal by 04z. Otherwise...varying degrees of middle level
moisture can be expected...at or above 6-8kft for the most part into Monday.
Winds will remain 10-12 knots or less into tonight...backing from
south-southwest to southeast late today. Tightening gradient will lead to gustier south-southwest
flow on Monday with gusts into the 25-30 knot range by middle/late
//Dtw threshold probabilities...
Lake Huron...Small Craft Advisory from 2 PM to 10 PM EDT Monday for lhz421-422-
Lake St Clair...Small Craft Advisory from 10 am to 10 PM EDT Monday for lcz460.
Michigan waters of Lake Erie...Small Craft Advisory from 10 am to 10 PM EDT
Monday for lez444.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).