Scientific Forecaster Discussion
fxus62 kmlb 222058
Area forecast discussion
National Weather Service Melbourne Florida
358 PM EST Mon Jan 22 2018
h100-h70 anticyclone centered just SW of Bermuda will retreat
into the central Atlc as a vigorous storm system over the Central
Plains lifts into the Great Lakes and Cranks a cold front into the
ern Gomex/Florida Panhandle. H100-h70 winds shifting to S/SW will pull
deep moisture up from the Florida Straits, while moisture pooling
within the frontal trof advances from the west. Pre- frontal
squall line will push into the I-4 corridor aft midnight, working
its way south of I- 4 in the predawn hours.
Rap40 analysis of the h30-h20 lyr shows a 130kt zonal jetstreak
centered over the arklatex that is preparing to shift to a lifting
orientation, while 850 mb-h30 analysis shows noteworthy vorticity, but
hardly off the charts. Mid lvl Omega/upr lvl divergence values much
stronger, but localized, suggesting these are more a product of
existing convection rather than a component of strong dynamic
Sfc dewpoints have climbed into the m60s, while model soundings/time
sections show dry/stable mid lvl air over central Florida modifying in a
"top-down" manner with h50 temps cooling from -7c/-8c to -10c/-11c.
These will combine to provide sufficient low/mid lvl instability to
keep a slgt chc of tsras in the fcst from the I-4 corridor
northward, but the timing of the squall line at the nocturnal
heating min along with the limited synoptic lvl forcing will keep
shras as the dominant form of precip...likely from Cape
Canaveral/lake-k northward, chc to the south. Light southerly winds
and increasing cloud cover will keep min temps in the l/m60s...arnd
15f abv avg.
warm S/SW flow will continue over much of central Florida as the cold
front works its way thru central Florida thru the day, eventually
reaching the Florida Straits by 12z Wed. Despite mcldy skies, the
strong warm air advection will push Max temps into the
M/u70s...near 80f south of Cape Canaveral and the Orlando
metroplex. The low lvl instability will combine with pwat values
btwn 1.50"-1.75" areawide to produce nmrs shras/isold tsras
areawide thru early aftn.
Pops diminishing to chc/slgt chc over the I-4 corridor/space coast
as the band advances into south FL, but remaining likely over the
Treasure Coast/lake-o region through sunset. By sunset, the parent
low expected to be over the New England/southeast Canada region with
flattening mid/upper flow acrs the Florida Peninsula, forcing the front
to gradually stall over South Florida/Florida Straits...chc/slgt chc of shras
lingering south of Cape Canaveral/lake-k Tue night.
Tuesday night-Wednesday night...
cold front will continue to push through the area and will have
effectively moved to our south late Tuesday night with cooler and
drier air beginning to move in behind it. Out ahead of the front,
keeping a chance of showers from vero southward (30-40%) and
slight chance (20%) extending north to Melbourne.
High pressure building over the Gulf Coast states during the day
Wednesday will continue to advect drier and cooler air into central
Florida. A large moisture gradient will be in place with pwats
forecast to be around 0.50" north of a line from Kissimmee to the
cape and increasing to around 1.50" for St. Lucie and Martin
counties. Only advertising a slight chance of showers from roughly
Okeechobee to Vero Beach southward where the lingering higher
moisture and weak convergence could generate a few showers. For
Wednesday night only keeping a slight chance of showers for Martin
County before the dry air wins out to put an end to precip chances.
Local pressure gradient will begin to tighten Wednesday night
producing breezy conditions along the coast.
Temperatures on Wednesday morning will start out quite cool and
range from the mid-upper 40s in the far northern areas (northern
lake and volusia) to the low 60s across the Treasure Coast. High
temperatures will be in the mid 60s to around 70. Even cooler
Wednesday night into Thursday morning with temps ranging from the
low-mid 40s north to the low-mid 50s to the southern areas.
rather strong Post-frontal high pressure centered over the
deep south will slide off the mid Atlantic coast on Fri. This will
cause a steady veering of winds from north/northeast early Thu, to
east on Fri and east/southeast Sat. A 5-6mb pressure gradient will
be maintained along the Florida East Coast, so conditions look to be
on the breezy side, especially the coastal counties. Substantial
drying is progged to occur Thu as precipitable water drops to about
a half inch or less. Therefore, the breezy onshore flow will take
a while to moisten the lower levels and bring small coastal shower
chances. MOS pops have values below 20 percent until Sat night, so
we'll just have minimal coastal rain chances in our forecast on Sat.
Temperatures will be cooler than normal Thu with lows mostly in the
40s to around 50 and highs in the 60s. Readings will then steadily
modify and be above normal on Sat with lows in the 50s to around
60 degrees and highs in the lower to mid 70s.
as the rather strong high pressure ridge retreats seaward,
the next frontal system will advance into the local area. The 12z
models show most of the energy associated with the shortwave trough
aloft moving by to our north, leaving the southern portion of the
frontal boundary to slow down slightly as it crosses our area.
Divergence aloft associated with the right rear quadrant of a jet
core exiting the mid Atlantic coast, and high moisture convergence,
should bring a period of high rain chances. We'll have to see if
the slightly slower trend continues, but right now the greatest
rain chances should be Sunday afternoon/night. It's too far out to
be certain of the impacts of this front, but there appears to be
some potential for locally heavy rain.
Sfc winds: thru 23/02z...E/se 7-11kts. Btwn 23/02z-22/05z...bcmg
S/southeast 4-8kts. Btwn 23/09z-23/12z...bcmg S/SW 3-6kts. Btwn 23/13z-
23/16z...bcmg S/SW 8-12kts.
Vsbys/wx/cigs: btwn 23/00z-23/06z...west of ktix-Kobe slgt chc MVFR
shras...north of kdab-klal chc MVFR shras/slgt chc IFR tsras. Btwn
23/06z-23/12z...north of kism-ktix MVFR cigs btwn fl020-030 areas IFR
cigs btwn fl005-009 IFR shras lkly/slgt chc LIFR tsras...S of kism-
ktix cigs btwn fl040-060 LCL MVFR cigs btwn fl020-030 chc IFR shras.
Aft 23/12z...MVFR cigs btwn fl020-030 IFR shras lkly/slgt chc LIFR
tonight...high pres ridge centered just SW of Bermuda will drift
seaward in advance of a cold front currently pushing acrs the lwr MS
valley. Storm system over the central Continental U.S. Will crank the frontal
boundary into the ern Gomex/NE Florida by daybreak Tue, then into the
Volusia waters by sunset, then into the Florida Straits Tue night.
Sfc/bndry lyr winds will gradually veer from a gentle to moderate
east/southeast breeze this evng, to due south by daybreak Tue. Seas 3-4ft.
Shras likely/slgt chc tsras over the Volusia waters, chc of shras
south of Brevard-Volusia line.
Tuesday...winds diminishing to a light to gentle breeze with the
approach of the frontal boundary, holding S/SW ahead of it, veering
to west/northwest behind it. Seas 3-4ft, except 2-3ft over the nearshore
Treasure Coast. Shras likely/slgt chc tsras thru midday, diminishing
to a chc/slgt chc of shras behind the fropa.
Wed-Sat...a cold front will settle into South Florida on Wed and
Florida Straits on Thu while rather strong high pressure builds
across the southeast states and shifts offshore into the
Atlantic. This will produce a tightening of the pressure gradient
over the waters while winds steadily veer from north on Wed to
east-southeast Sat. Wind speeds will increase to 15-20 knots Wed
night and then be around 20 knots through Sat. Conditions for
small craft operation will become poor by Wed night, then become
hazardous Thu into Sat.
Preliminary point temps/pops...
dab 64 74 48 64 / 70 60 10 0
mco 66 77 55 69 / 60 60 10 10
mlb 65 77 60 68 / 40 70 20 10
vrb 65 78 60 69 / 30 70 20 20
Lee 66 75 51 68 / 70 60 10 10
sfb 65 76 53 67 / 70 60 10 10
orl 66 77 55 69 / 70 60 10 10
fpr 65 78 62 70 / 30 70 30 20