Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
402 am EDT Sat may 23 2015
Short term...today and tonight
Exceptional weather is the message of the day as a surface ridge
axis remains parked over southeastern Michigan. The near surface
ridging under building heights aloft provide a Road block for true
return flow to become established. The main question is one of cloud
cover. A modest upper level jetlet is forecasted to ease northward
during the course of the day...becoming settled over southeastern
Michigan for the afternoon hours. This should serve as a conduit for
high cloud cirrus. With satellite imagery this morning showing
plenty of cloud spilling as far northward as the I 69 corridor...the
plan is to increase amount of sky cover in the grids for today.
Determining opacity is always fun overnight...but given the
observational evidence in addition to some model support will
increase to partly cloudy. Despite less insolation...airmass
moderation supports forecasting temperatures in the lower 70s today
Deep ridging tonight with an influence from an upper level
anticyclonic flow trajectory will maintain quiet weather tonight.
Increasing high cloud should be fairly aggressive with the
aforementioned jetlet positioned overhead. Temperatures tonight will
be considerably warmer with readings running in the 50s.
Long term... Sunday through Friday
Broad middle/upper level trough will persist over the western Continental U.S.
Through the upcoming week while ridging over the southeast Continental U.S. Tries to
hold over the East Coast and into the eastern Great Lakes. This
setup puts Southeast Michigan in the cross hairs for deep layer SW flow through
middle week until the trough tries to break down. Additional wave
entering the trough early in the week will slowly work keeping some
semblance of the trough intact keeping the swerly flow going. This
warm and moist airmass will present several opportunities for shower
and thunderstorm development as a series of waves exiting the trough
lift through southern Michigan. Timing these individual waves will be key
on zeroing in on most likely periods of wet weather. This task is
difficult at best in this scenario...complicated further by
orientation and timing of the larger upper level features within the
trough. Though the forecast will read chance of showers and
thunderstorms almost every day through the coming week...it should
not be a total washout. Will adjust for wet and dry periods as the
small scale features can be resolved.
First opportunity for precipitation will be Sunday evening as an strong
upper low lifting into the middle west sends a Wing of isentropic
ascent up through the state...with upper level support from a
developing jet streak over the northern Great Lakes. The right
entrance region will Colorado-locate with the region of isentropic ascent
Sunday evening. The bulk of the activity looks to hold over northern
lower Michigan but timing suggests it could clip Saginaw Valley and the
The Thumb on its way north before stalling across northern lower.
Will trim likely probability of precipitation to the Saginaw Valley region in the late
afternoon/evening with high chance probability of precipitation extending southward. May be
able to trim further...at least through the earlier part of the day
if the upper level features slow down further as they did the last
model cycle or two. High pressure at the surface will keep the activity
mostly elevated and non severe.
Next good chance for showers and thunderstorm will come on Monday as
a warm front lifts north through Michigan. The ridge axis will also pass
to the east allowing precipitable waters to surge over 1.5 inches with enhances ll
jet surging into the region with roots reaching into the gom. This
flow and pattern will continue through Wednesday as the trough
continues to release shortwaves into the area before the strongest
upper level energy pushes off into Canada. Warm and moist flow will
continue through the end of the week as new upper level wave works
across the Continental U.S. Keeping weak troughing in place.
Large area of surface high pressure now centered over the East Coast
will keep its northwest quadrant covering the eastern Great Lakes
through tonight. This will result in light winds and low waves into
Sunday. Temperatures will be on the rise through the weekend as
southwesterly flow brings warm and humid air into the region.
Chances of showers and thunderstorms will begin late Sunday and
persist through the beginning of next week as this airmass remains
Aviation...issued 1155 PM EDT Friday may 22 2015
Other than a few high clouds...high pressure will sustain mainly
clear skies and light winds through the morning. The departure of
the surface high to the east on Saturday will lead to a development of
some modest south-southwest winds by in the afternoon.
//Dtw threshold probabilities...
Michigan...frost advisory until 8 am EDT this morning for miz047>049-053>055-
Lake St Clair...none.
Michigan waters of Lake Erie...none.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).