Basicsofweatherinterpretation
SafetyatSeaSeminar, April2nd 2016
Dr.GinaHenderson
Oceanography Dept.,
USNA
ghenders@usna.edu
Imagesource:http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=80399,accessed03/03/13
Thegoalofthissessionis
to:
§ Understandmainfeatureson
asurfaceweatherchart
§ Cloudinterpretationasit
relatestosailingconditions
§ SevereweatherontheBay&
enroutetoBermuda
§ Introduceupperatmospheric
chart@500mb specifically
Imagesource:www.opc.ncep.noaa.gov
Weatherproductsfrom
NOAAOceanPredictionCenter
Weatherproductsfrom
NOAAOceanPredictionCenter
Weatherproductsfrom
NOAAOceanPredictionCenter
Letusidentifysome
featuresonthis
SurfaceAnalysismap:
Imagesource:
www.opc.ncep.noaa.gov
Letusidentifysome
featuresonthis
SurfaceAnalysismap:
§
§
§
§
Surfacemap
“ISSUED”
à timeanalysiswas
released
“VALID”
à Timeconditions
apply
UTC/GMT/Zulutime
Imagesource:
www.opc.ncep.noaa.gov
Letusidentifysome
featuresonthis
SurfaceAnalysismap:
§ H vs.L?
§ H vs.Lrelativeto
what?
Meansealevelpressure
à 1013millibars
§ Pressuregradients?
§ Fronts?
Imagesource:
www.opc.ncep.noaa.gov
Pressuregradients:
Atthesurfacewindscrosstheisobarstoward
lowpressure andawayfromhighpressure
SurfaceHighpressurecenter SurfaceLowpressurecenter
§
§
Windsdivergeatcenter
Clockwise(anticyclonic flow)
§
§
Windsconvergeatcenter
Counter-clockwise(cyclonic
flow)
Wind101
§ Windà horizontalmovementofair
§ ‘Naming’wind
o Fromsourcedirection
Wind101
§ Measuringwindspeed
o Knots
o MPH
o BeaufortScale….“force1-12”
PressureGradient
§ Increasedgradientà increasedwindspeed
Letusidentifysome
featuresonthis
SurfaceAnalysismap:
§ Wherearethe
strongestwindson
thischart?
§ Whatdirectionare
theyflowing?
Imagesource:
www.opc.ncep.noaa.gov
Letusidentifysome
featuresonthis
SurfaceAnalysismap:
§ Interpretinga
stationmodel
Imagesource:
www.opc.ncep.noaa.gov
Letusidentifysome
featuresonthis
SurfaceAnalysismap:
§ Interpretinga
stationmodel
Imagesource:
www.opc.ncep.noaa.gov
Interpretingastationmodel
Interpretingastationmodel
Interpretingastationmodel
Interpretingastationmodel:
Whatinformationarewegiven?
§
§
§
§
§
§
§
§
Surfacepressure(upperright)
Pressuretendency(notshownhere)
Waveheight(lowerright)
Temperature(upperleft)
Dewpointtemp(lowerleft)
Windspeed&direction
Skyconditions(middle)
Seasurfacetemp(lowermiddle)
Interpretingastationmodel:
Whatinformationarewegiven?
10.9
109
Pressurerangeis960mb to1060mb.Youmustdecideifa9or10
shouldgoinfrontofthepressure.
Interpretingastationmodel:
Whatinformationarewegiven?
Inthiscase
10.9
1010.9mb
109
Pressurerangeis960mb to1060mb.Youmustdecideifa9or10
shouldgoinfrontofthepressure.
Interpretingastationmodel:
Whatinformationarewegiven?
§
§
§
§
§
§
§
§
Surfacepressure(upperright)
Pressuretendency(notshownhere)
Waveheight(lowerright)
Temperature(upperleft)
Dewpointtemp(lowerleft)
Windspeed&direction
Skyconditions(middle)
Seasurfacetemp(lowermiddle)
Whatcancloudstellusabout
approachingweathersystems?
Skyconditions:
Cloudtypes&identification
Namedbasedon:
§ Height
§ Shape
Cirrus=thinandwispy
Stratus=flatcloudsinlayers
Cumulus=puffycloudsinheaps
Nimbostratus =rain(greyincolor)
Cumulonimbus=thunderstorm
4maintypesofthunderstorms,dependingonhow
organizedthesystemis…...
1. Airmass à awayfromfrontalboundary
§ driven byintense surface heating, rarelyproduceshail/tornadoes
2. Squall lineà alineofstorms,often alongafrontalboundary
§ Associated withheavyprecipitation, windsandpotentiallyhail/tornadoes
4maintypesofthunderstorms,dependingonhow
organizedthesystemis…...
3. Multi-cell à storms occurinclusters
§ Mostcommoninspring/summer
4. Supercellà mostintense andsevere
§ Supercell thunderstorm updraftsALWAYS rotate
Thunderstormclouds
-- greentingemayindicatepresence
ofhail
Thunderstormclouds
-- Hookecho,Tulsa03/30/16
SquallLine
§ Longlineofthunderstorms
o individual“cells”aresoclosetogethertheheavy
precipitationformsalongcontinuousline
§ Typicallyformalonganadvancingcoldfront
o Sometimesassociatedwithacoldfrontaloft
§ Canbehundredsofmileslong
§ Mostcommonlyassociatedwithstrongstraight-line
winds
o Canproducehailand/ortornadoes,too
§ Called“squall”becauseoftheabruptwindchanges
SquallLines
Squalllinethunderstorms
SquallLines
Squalllinethunderstorms
L
Squallline
approaching
Memphis,TN.
Notetheheaviest
precip isalongthe
leading(eastern)
edgeoftheline,
withmoderate– but
stillcontinuous –
rainfalloccurring
100+kmbehind(to
thewest)ofthe
“line”
Shelfcloud:foundalongtheleadingedge
ofthegustfront
SquallLines
SquallLines
Letusidentifysome
featuresonthis
SurfaceAnalysismap:
§ Pressuregradients
§ Fronts?
Afrontisatransition
zonebetweentwoair
massesofdifferent
temperatureand
moisturecontent(they
havedifferentdensities)
Imagesource:
www.opc.ncep.noaa.gov
AirMasses
haveuniformtemperature&moisturecharacteristics
Figure 5.21
Letusidentifysome
featuresonthis
SurfaceAnalysismap:
Fronts,4maintypes
1. Astationaryfront
2. Acoldfront
3. Awarmfront
4. Anoccludedfront
Imagesource:
www.opc.ncep.noaa.gov
Midlatitudecyclones=clashoftwodifferentairmasstypes!
Imagesource:http://www.hpc.ncep.noaa.gov/sfc/usdwmsfcbw.pdf, accessed04/01/14
§ Letuscomparethesurfaceobservations
ahead,andbehindthefront
StationaryFront
Coldair
.
X
Warmair
§ Cloudtypesdependonthe
atmosphericstability
§ Precipitationintensity
dependsonthesituation
ColdFront
marksthe“front”ofacoldairmass
§ Howisitrepresented onamap? § Whattypeofclouds andweatherisitassociated with?
WarmFront
marksthe“front”ofawarmairmass
§ Howisitrepresented onamap? § Whattypeofclouds andweatherisitassociated with?
OccludedFront
§ Cloudsand
precipitation depend
ontheatmospheric
stability
Thefollowing criteria
areusedtolocate
fronts:
1. Sharptemperature
changes
2. Sharpdewpointchanges
3. Windshiftlines
4. Pressurechanges
(pressure“tendency”)
5. Thepresenceofclouds
andprecipitation
cP
mP
cT
mT
Thefollowing criteria
areusedtolocate
fronts:
1. Sharptemperature
changes
2. Sharpdewpointchanges
3. Windshiftlines
4. Pressurechanges
(pressure“tendency”)
5. Thepresenceofclouds
andprecipitation
Interpretingastationmodel:
Whatinformationarewegiven?
§
§
§
§
§
§
§
§
Surfacepressure(upperright)
Pressuretendency(notshownhere)
Waveheight(lowerright)
Temperature(upperleft)
Dewpointtemp(lowerleft)
Windspeed&direction
Skyconditions(middle)
Seasurfacetemp(lowermiddle)
Waterholdingcapacityof
atmosphere…..
Amountofwaterinatmosphere….
Dewpointdepression=T- TD
Imagesource:http://www.hpc.ncep.noaa.gov/sfc/usdwmsfcbw.pdf, accessed04/01/14
Howdoweforecastwheresurface
systemswillmove?
LookUP!
Letusidentifysome
featuresonthis
SurfaceAnalysismap:
§ Wherewillour
surfacesystems
moveto?
§ Willtheyintensify
orweaken?
Imagesource:
www.opc.ncep.noaa.gov
500mbChart:forecast
-- Givesustheheightwherewereach500mbofpressure
500mbChartvs.Surfacechart
500mbChart:forecast
-- Alsocalledthe‘steeringlevel’oftheatmosphere
LetustrackwhereoursurfaceLowandsurfaceHigh
go…...
L
H
24-hourforecastedsurfacemap
Weatherproductsfrom
NOAAOceanPredictionCenter
24-hourwind&waveproduct
24-hourwind&waveproduct
Waveheight (ft)=totalheightfromcresttotrough
Hurricanes
AtlantichurricaneseasonrunsfromJune1sttoNovember30th
Hurricanes
AtlantichurricaneseasonrunsfromJune1sttoNovember30th
Thegoalofthissessionis
to:
ü Understandmainfeatureson
asurfaceweatherchart
ü Cloudinterpretationasit
relatestosailingconditions
ü SevereweatherontheBay&
enroutetoBermuda
Dr.GinaHenderson
OceanographyDept.,USNA
ghenders@usna.edu
ü Introduceupperatmospheric
chart@500mb specifically
Imagesource:www.opc.ncep.noaa.gov