Aviation Forecasts Discussions (AFD) INFO

(EXTRACTED FROM FXUS64 KMOB 231545)


    12Z issuance...With continued moist flow off the Gulf, IFR to LIFR
    CIGs/VISBYs will generally rise into MVFR levels before settling
    back into IFR to LIFR levels again tonight. With seemingly ever-
    present subsidence inversion less of a limit this afternoon, ts
    mixing in with shra this afternoon/evening.
    
    /16
    
    PREV DISCUSSION... /issued 451 AM CST Fri Feb 23 2018/
    
    NEAR TERM /Now Through Friday night/...An upper ridge present
    over the  Gulf and Caribbean will continue to get a squeeze as
    yet more shortwave energy moves through an upper trough centered
    over the western Conus. A surface ridge that has been maintained
    by the upper ridge does continue to maintain its position
    stretching west over the northern Gulf coast, continuing to bring
    a light to moderate onshore flow over the forecast area through
    the near term. Looking at model soundings for the area, light
    onshore flow that has set up overnight will continue into the
    morning hours, then as the land begins to warm, shra begin to
    form. A weakening subsidence inversion centered around 700 mb
    limits the vertical extent of the showers, though. As afternoon
    approaches, guidance is advertising the subsidence inversion
    becoming less of a limiter, so am expecting tsra begin to mix in
    into the early evening hours. After the sun sets, precip coverage
    decreases. Overnight fog development is expected to continue,
    though with water temps along the coast on the increase, dense fog
    will be less clear cut.
    
    For temps, with the upper high still maintaining its presence,
    albeit less strong then earlier this week, above seasonal temps
    continue.
    
    With the warm temps allowing for more persons to visit area beaches,
    a moderate onshore flow continues. Adding in a wide tidal cycle,
    have issued an RP.S for a high risk of dangerous rip currents over
    area beaches. /16
    
    SHORT TERM /Saturday Through Sunday night/...An elongated upper
    level ridge of high pressure extending from southern Mexico
    northeast across the Florida peninsula to the western Atlantic
    will drift very slowly to the southeast. This southeast drift is
    in response to two upper level shortwaves exiting the Rockies
    through the near term. The first upper shortwave will lift
    northeast over the central and northern Great Plains toward the
    western Great Lakes on Saturday, followed by a second shortwave
    moving eastward over the Great Plains toward the Mississippi River
    on Sunday.
    
    Meanwhile, a surface high pressure ridge across the southeast
    states and northeast Gulf of Mexico will also drift southeastward
    and weaken in response to a series of surface low pressure areas
    passing northwest of the forecast area. A light southerly wind
    flow will persist across the forecast area between these features
    through Sunday evening, followed by a cold front moving into the
    forecast area late Sunday night. Isolated to scattered showers and
    thunderstorms will occur on Saturday, with numerous to definite
    showers and thunderstorms occurring on Sunday.
    
    A strengthening upper level jet max of 130 to 160 knots ahead of
    the second upper shortwave will form over the eastern conus, while
    a low level jet of 20 to 40 knots is expected to develop over
    weekend. Maximum mixed layer CAPE values over the weekend are
    forecast to range from 150 to 300 J/kg, with maximum SFC-1km SRH
    values forecast to range from 100 to 200 M2/S2. Still expect a
    few strong to marginal severe thunderstorms during the day
    Saturday northwest of I-65, and across the entire forecast on
    Sunday, with strong thunderstorm wind gusts the main threat.
    
    Patchy fog will linger into Saturday morning, with near record
    high temperatures on Saturday climbing into the low to mid 80s,
    except for the upper 70s along the immediate coastal sections.
    /22
    
    LONG TERM /Monday Through Thursday/...The cold front will move
    southeast of the forecast area on Monday, with the showers and
    thunderstorms quickly decreasing from northwest to southeast
    Monday morning as a much drier airmass spreads into the area in
    the wake of the front. Drier weather is expected Monday night
    along with noticeably cooler temperatures, before rain chances
    increase Tuesday into mid week ahead of the next approaching
    shortwave trough. Another shortwave trough and associated cold
    front could then bring the next round of showers and possibly a
    few storms Thursday. Above normal temperatures are expected
    Tuesday through Thursday. /22
    
    MARINE...A surface ridge will continue to stretch west over the
    northern Gulf coast into Sunday, bringing light to moderate
    onshore flow. Fog development will continue with the onshore
    flow, though dense fog will have to play by ear with water temps
    on the rise due to the southerly flow. A front will move south,
    then stall along the northern Gulf coast late Sunday through
    Sunday night, bringing unsettled weather. A passing upper system
    will push the front south of the coast Monday night, bringing a
    small period of offshore flow late Monday night into Tuesday
    before a surface ridge becomes re- established over the Southeast
    Tuesday night. /16