Scientific Forecaster Discussion
Area forecast discussion
National Weather Service northern Indiana
541 am EDT Sat Aug 30 2014
issued at 107 am EDT Sat Aug 30 2014
Today will feature warm and humid conditions as a warm front lifts
north of the area. Skies will be mostly cloudy with highs likely
reaching the 80s. Scattered showers and thunderstorms will be
possible by mainly this afternoon and evening as low pressure
tracks into the Great Lakes region. Drier air will briefly work
into the area on Sunday before a cold front brings renewed chances
for showers and thunderstorms on Monday. Highs on Sunday and
Monday are forecast to reach the low to middle 80s.
Short term...(today and tonight)
issued at 438 am EDT Sat Aug 30 2014
Main focus remains convective chances and severe/flooding threat
mainly later this afternoon/evening...
An upper Midwest shortwave trough and attendant weak surface reflection
will shear east-northeast into the northern lakes later today into tonight.
Strengthening unidirectional SW flow in the lower half of the
troposphere (associated with 40-60 meter 500 mb height fall centroid
track into WI/northern lower Michigan today) will likely allow warm sector
to become fully established across the area later this morning. Did
retain low-middle chances for isolated-scattered showers/embedded thunder mainly
west of I-69 this morning/early afternoon given continued low level
Theta-E advection within llj, lingering MUCAPE, and northeastward track of a
subtle western Ohio/middle MS valley middle level impulse east-northeast into the area.
Cloud cover and meager middle level lapse rates will likely limit degree
of boundary layer destabilization a bit within warm sector.
However...surface dewpoints near 70f and expected breaks in overcast
should still support 1000-1500 j/kg of MLCAPE by this afternoon.
Moisture quality for convective development appears more than
sufficient with early morning water vapor showing plume of deeper
tropical moisture (13-14 g/kg within 925-850mb layer) advecting this
way from the Lower/Middle MS valleys. Low/middle level forcing not overly
impressive with northerly track of primary shortwave sending a
weakening convergent boundary into our northwest zones middle afternoon-early evening.
This feature and additional vorticity energy swinging through base of
trough...combined with ample moisture...will likely still be enough
to help focus scattered showers/storms during this time. An isolated
strong-severe storm (damaging winds primary threat) appears possible
mainly west-northwest of I-69 later this afternoon given some middle level drying
and modest/unidirectional deep layer shear values to 30-35
kts...with paltry middle level lapse rates and questions regarding
cloud cover the main limiting factors for a more widespread
Pre-frontal boundary/outflow will attempt to slowly settle southeast into
central/southern portions of the forecast area this evening/early overnight
under prevailing/weakening west-southwest flow aloft. High moisture content,
skinny/dwindling Cape, Small mbe vectors, and warm cloud layer to 12
kft all hint at the potential for locally heavy rainfall/flooding.
Will continue to highlight this potential in the severe weather potential statement.
Otherwise...warm/humid this period with only minor tweaks to temperatures.
Long term...(sunday through friday)
issued at 438 am EDT Sat Aug 30 2014
Few changes in early part of long term focus. Anticipate well
scoured middle level moisture along with overturned airmass into Sunday
across County Warning Area along with interlude of short wave ridging in wake of
energy /currently across upper MS valley/ lifting northeastward into Quebec.
Given more favorable intermodel agreement as opposed to yesterday
at this time...thunderstorms and rain chances Monday afternoon into evening appear on
the increase. Deep west coastal wave to track eastward through
northern plains Sunday night...then increasingly negatively tilted
through upper Midwest/upper Great Lakes by Monday afternoon/evening.
Middle level westerly flow increases to 45-50kts across southern Great
Lakes on southern periphery of shortwave. Suspect strong airmass
recovery/destabilization within prefrontal warm sector into Monday
afternoon with thermal ridge axis poised from central Illinois into
Michigan thumb...culminating with peak sbcapes in 2500-3000 j/kg per
NAM/wrfarw modified point soundings across northern Indiana in 21-24
UTC timeframe. Suspect convection to have maintenance with favorable
upper jet dynamics and sufficient downstream instability well
through the late evening into eastern County Warning Area. Potential
organization/cold pool congeal with primary wind risk
associated...with secondary/lesser hail threat owing to warm wetbulb
zero heights. Continued chance thunderstorms and rain /highest S/ with frontal boundary
potentially lying out east-west through southern County Warning Area to i70 corridor. With
potential for frontal wave that should slow frontal boundarys S/southeastward
progress...especially per European model (ecmwf) vs GFS. Amid lackluster gefs average
probability of precipitation vs climatology and gradual middle week rising heights favor to eschew
dry period vs consensus upward pop creep...Tuesday night into
Thursday...until next/more substantive wave tracks through upper MS
valley/northern Great Lakes Thursday night into Friday with surface
frontal boundary to take southeast sag through County Warning Area to near Ohio
River valley about next Saturday.
Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 541 am EDT Sat Aug 30 2014
Mainly VFR today into this evening outside of convection. Scattered
showers/isolated thunder associated with a surge of deeper moisture and
approach of a subtle middle MS/Ohio Valley wave may work east-northeast through
northern Indiana this morning/early afternoon...best chances
11-15z at ksbn and 14-18z at FWA. This high based activity should
have little impact on the terminals. A frontal boundary on the
southeastern fringe of height falls/upper trough lifting into the
northern lakes will overspread an increasingly moist/unstable boundary
layer. A line of broken convection should accompany this feature
and edge east-southeast into the area later this afternoon/evening.
Otherwise...southwesterly winds will pick up to near 15 kts today.
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