Scientific Forecaster Discussion
fxus63 kdtx 240352
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1152 PM EDT sun Jul 23 2017
Steady southward expansion of low stratus expected overnight as a
cold front effectively shifts the deep moisture plume out of the
state. Upstream satellite and observational trends suggest ceiling
bases will arrive at IFR or lower MVFR during the early and mid
morning period. A drying environment along with daytime mixing
will lift ceilings through the afternoon. Modest northwest wind
becoming northerly on Monday.
For dtw...timing on the cold front and arrival of MVFR ceiling
remains centered during the mid morning hours /10-11z/. Cigs below
5000 ft likely thru early tomorrow afternoon.
//Dtw threshold probabilities...
* high for ceiling at or below 5000 feet late tonight through Monday
issued at 325 PM EDT sun Jul 23 2017
Regional satellite data show a compact mid level low rotating into
ern upper mi/ern Lake Superior. There is good agreement among the
12z model suite in showing this low advancing into ern Ontario/SW
Quebec tonight through Monday as an open wave. The associated mid
level height falls have been pushing across lower mi all day. There
are now indications in radar that the cap over se mi is being
eroded. The 18z meso analysis shows a region of enhanced sfc
convergence along the I-94 corridor and to some extent across
western lower mi (where a trough is developing in the Lee of lake
michigan). It is this trough that is expected to enhance low level
convergence as it slowly pushes east into se mi late this afternoon
and evening. Thus, scattered to numerous coverage of
showers/thunderstorms can be expected as this sfc convergence
interacts with the moist and moderately unstable environment over se
mi, primarily through 00z.
Taking into consideration latest sfc observations and Storm Prediction Center meso
analysis, 0-1km MLCAPE looks to be between 1000 and 1500 j/kg. With
700-500mb lapse rates around 6 deg c/km and 0-6km bulk shear values
near 30 knots, given the ample moisture and marginal wind shear,
expect convective Mode to be primarily multi cell clusters with some
embedded strong to severe thunderstorms. Strong winds and hail
appear the greatest severe concerns. The sfc trough axis and
instability is expected to slide east of the forecast area in the 00
to 03z time frame, with mid level dry airexpanding across the area.
This will end the risk of additional convection by late evening.
Sfc low pressure is forecast to consolidate over the ern Great Lakes
tonight into Monday, while sfc troughing holds across srn Lake
Huron. This will support low level cyclonic flow across the area
through the day Monday. The region of low clouds now blanketing
Upper Michigan will slide across Lake Huron and nrn lower mi tonight
before filtering into se mi early Mon morning. The low level
cyclonic flow combined with the added moisture flux off Lake Huron
within a low level thermal trough will support extensive cloud cover
through much of the day Monday. The degree of low level moisture is
such that areas of drizzle and/or light showers may affect portions
of the northern sections of forecast area late tonight into Monday,
with The Thumb region likely seeing more persistent light showers
off the lake. Within the low level thermal trough and cloud cover,
Monday highs will remain in the 70s (upper 60s along lake huron).
Mid level ridging and sfc high pressure will expand across lower mi
Mon night into Tuesday, bringing much drier conditions to area.
The next round of active weather will arrive late Wednesday into
Thursday as a cold front pushes through the region. Ahead of the
front on Wednesday, increasing southwest flow as high pressure
departs the region will bring warmer, more humid conditions with
highs in the mid to upper 80s. A period of showers and thunderstorms
is expected ahead of the frontal passage Wednesday night into
Thursday. Frontal passage timing varies slightly among model
guidance with the European model (ecmwf) favoring a later passage on Thursday while
the GFS and Gem favor an earlier passage on Thursday morning. High
pressure then builds back into the region Friday into next weekend
bringing a return to dry, pleasant conditions with highs ranging
from the mid 70s to lower 80s and lows in the mid 50s to lower 60s.
The relatively weak winds across the region this afternoon are the
result of a broad region of disorganized low pressure centered over
lower Michigan. This low will slide across the eastern Great Lakes
tonight and will deepen across Lake Ontario on Monday. A surface
trough axis will reside across far Southern Lake Huron into Monday
morning before pulling east Monday afternoon. There will be an
enhanced north-northeasterly gradient on the back side of this sfc
trough across Lake Huron. Cooler air overspreading the relatively
Warm Lake will also boost mixing depths. The result will be a push
of stronger winds (20 to 30 knots) across Lake Huron tonight
through the day Monday. This will support increasing wave heights
and rough conditions for small craft, especially across Southern
Lake Huron. Winds and waves will then decrease Monday night into
Tuesday as high pressure builds in from the west.
Michigan...Beach hazards statement from 8 am EDT Monday through Monday evening
Lake Huron...Small Craft Advisory from 6 am to 8 PM EDT Monday for lhz421-422-
Small Craft Advisory from 10 am Monday to 4 am EDT Tuesday for
Lake St Clair...none.
Michigan waters of Lake Erie...none.