SURFACE DATA AND WEATHER FEATURES MSC 243 Lecture #2 09/03/13.

SURFACE DATA AND WEATHER FEATURES

MSC 243 Lecture #2

09/03/13

Recap from last week• MOS is a combination of computer model output

(run on supercomputers) and bias corrections. Models: GFS (AVN), NAM (ETA).

• While MOS is a good “first guess” at point forecasts for cities, it is not the only thing we should examine.

• Over the next few lectures, we look at the main weather observations used to find current conditions and to make short-term forecasts.

This Lecture

• ASOS / METAR Observations• Decoding METAR• Verification of last Thursday’s Lab• Surface Station Models• Pressure-Wind Relationship

Surface Weather Analysis

http://www.hpc.ncep.noaa.gov

Surface Observations• Automated Surface Observing System (ASOS)• Automated Weather Observing System (AWOS)

ASOS: http://www.nws.noaa.gov/asos/

http://en.wikipedia.org/wiki/Automated_airport_weather_station

• Instruments:– Tipping bucket (rain gauge)– Hygrothermometer (temp/dewpoint sensor)– Present Weather Identifier (precip/fog/haze)– Wind speed and direction sensors– Ceilometer (cloud height)– Freezing rain and thunderstorm sensors– Visibility sensor– Data collection, processing and transfer in

METAR format

Time and Temperature• Observations across the globe taken and

recorded using Universal time (UTC)– UTC = Greenwich Mean Time– Eastern Daylight Time = UTC – 4 Hours

• Temperatures reported using Celsius scale– F = (9/5)*C + 32– C = (5/9)*(F-32)

°C 0 5 10 15 20 25 30 35°F 32 41 50 59 68 77 86 95

METAR Observations

Example METAR Report METAR KABC 121755Z AUTO 21016G24KT 180V240 1SM R11/P6000FT

-RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T00640036 10066 21012 58033 TSNO $

KABC - ICAO STATION (location) IDENTIFIER Four character ICAO location identifier.

121755Z - DATE/TIME All dates and times in UTC using a 24-hour clock; two-digit date and four-digit time; always appended with Z to indicate UTC.

AUTO REPORT MODIFIER AUTO: Indicates a fully automated report with no human intervention. It is removed when an observer logs on to the system. COR: Indicates a corrected observation. No modifier indicates human observer or automated system with human logged on for oversight functions.

http://weather.cod.edu/notes/metar.html

METAR Observations

Example METAR Report METAR KABC 121755Z AUTO 21016G24KT 180V240 1SM R11/P6000FT

-RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T00640036 10066 21012 58033 TSNO $

21016G24KT - WIND DIRECTION AND SPEED Direction in degrees from true north (first three digits); next two digits: speed in whole knots; if needed, include character as: Gusts (character) followed by maximum observed speed; always appended with KT to indicate knots; 00000KT for calm

180V240 - if direction varies by 60o or more and speed greater than 6 knots, a Variable wind direction group is reported, otherwise omitted. If wind direction is variable and speed 6 knots or less, replace wind direction with VRB followed by wind speed in knots.

1SM VISIBILITY Prevailing visibility in statute miles and fractions with space between whole miles and fractions; always appended with SM to indicate statute miles; values <1/4SM reported as M1/4SM.

METAR Observations

Example METAR Report METAR KABC 121755Z AUTO 21016G24KT 180V240 1SM R11/P6000FT

–RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T00640036 10066 21012 58033 TSNO $

-RA BR - WEATHER PHENOMENA- Intensity or Proximity “-” Light, “no sign” Moderate, “+” Heavy, VC

Vicinity- Precipitation: DZ Drizzle, IC Ice Crystals, UP Unknown in automated

observations, RA Rain, PL Ice pellets, SN Snow, GR Hail, SG Snow grains GS Small hail/snow pellets

- Obscuration: BR Mist (< or = 5/8SM), SA Sand, FU Smoke, HZ Haze, VA Volcanic Ash, PY Spray, DU Widespread Dust

- Other: SQ Squall, FC Funnel Cloud, SS Sandstorm, +FC Tornado/ Waterspout, DS Duststorm, PO Well developed dust/sand whirls.

METAR Observations

Example METAR Report METAR KABC 121755Z AUTO 21016G24KT 180V240 1SM R11/P6000FT

–RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T00640036 10066 21012 58033 TSNO $

BKN015 OVC025 - SKY CONDITION. Cloud amount: Sky CLeaR 0/8; FEW 1/8-2/8; SCattered 3/8-4/8;

BroKeN 5/8-7/8; OVerCast 8/8; Cloud height: 3-digit height of base in hundreds of feet, followed by

Towering CUmulus or CumulonimBus if present. More than 1 layer may be reported.

(broken cloud deck at 1500 ft, then overcast at 2500 ft here)

06/04 - TEMPERATURE/DEW POINT. Each is reported in whole degrees Celsius using two digits; values are separated by a slash; sub-zero values are prefixed with an M (minus). Dew Point is the temperature which air must be cooled to in order to be saturated.

METAR Observations

Example METAR Report METAR KABC 121755Z AUTO 21016G24KT 180V240 1SM R11/P6000FT

–RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T00640036 10066 21012 58033 TSNO $

A2990 ALTIMETER. Altimeter setting (in U.S. reports) is always prefixed with an A indicating inches of mercury; reported using four digits: tens, units, tenths, and hundredths (29.90” Hg here).

RMK REMARKS IDENTIFIER. Remarks includes clarifying or augmenting data concerning elements in the body of the METAR, additive coded data and maintenance data.

AO2 TYPE OF AUTOMATED STATION. AO1; automated station without a precipitation discriminator. AO2; automated station with precipitation discriminator.

METAR Observations

Example METAR Report METAR KABC 121755Z AUTO 21016G24KT 180V240 1SM R11/P6000FT

–RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T00640036 10066 21012 58033 TSNO $

PK WND 20032/25 - PEAK WIND. PK WND dddff(F)/(hh)mm; direction in degrees, speed in whole knots / time in minutes after the hour. Only minutes after the hour is included if the hour can be inferred from the report.

WSHFT 1715 - WIND SHIFT. WSHFT followed by hours and minutes of occurrence. The term FROPA may be entered after the time if it is reasonably certain that the wind shift was a result of a frontal passage.

METAR Observations

Example METAR Report METAR KABC 121755Z AUTO 21016G24KT 180V240 1SM R11/P6000FT

–RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T00640036 10066 21012 58033 TSNO $

P0003 - HOURLY PRECIPITATION AMOUNT. Prrrr; in tens, units, tenths and hundredths of an inch since last regular hourly METAR. A trace is reported as P0000. (0.03” here)

60009 - 3- AND 6-HOUR PRECIPITATION AMOUNT. 6rrrr; precipitation amount, including water equivalent, to nearest 0.01 inches for past 6 hours reported in 00, 06, 12, and 18 UTC observations and for past 3 hours in 03, 09, 15, and 21 UTC observations. A trace is 60000. (0.09” in past 6h here)

7**** Not on this report - 24-HOUR PRECIPITATION AMOUNT. 7****; precipitation amount to nearest 0.01 inches for past 24 hours reported in 12 UTC observation; e.g., 70015 indicates 0.15 inches of precipitation for past 24 hours.

METAR Observations

Example METAR Report METAR KABC 121755Z AUTO 21016G24KT 180V240 1SM R11/P6000FT

–RA BR BKN015 0VC025 06/04 A2990 RMK A02 PK WND 20032/25 WSHFT 1715 VIS 3/4V1 1/2 VIS 3/4 RWY11 RAB07 CIG 013V017 CIG 017 RWY11 PRESFR SLP125 POOO3 6OOO9 T00640036 10066 21012 58033 TSNO $

T00640036 - HOURLY TEMPERATURE AND DEW POINT. TsnTaTaTa snT'aT'aT'a; reported to nearest tenth of oC; sn: 1 if temperature or dew point below 0oC and 0 if temperature/dew point 0oC or higher. (+6.4C / +3.6C here)

10066 - 6-HOUR MAXIMUM TEMPERATURE. 1snTxTxTx; maximum temperature for past 6 hours reported to nearest tenth of degree Celsius; reported on 00, 06, 12, 18 UTC reports; sn = 1 if temperature below 0oC and 0 if temperature 0oC or higher (max of +6.6C in past 6h here)

21012 - 6-HOUR MINIMUM TEMPERATURE. 2snTnTnTn; minimum temperature for past 6 hours reported to nearest tenth of degree Celsius; reported on 00, 06, 12, 18 UTC reports; sn = 1 if temperature below 0oC and 0 if temperature 0oC or higher. (min of -1.2C in past 6h here)

Lab 1: Flagstaff, AZ

• Based purely on GFS MOS Guidance• Your WXChallenge-style forecasts for

06 UTC Aug 30th – 06 UTC Aug 31st

Max Temp 78 FMin Temp 59 FMax Wind Speed 4 ktPrecipitation amount: 0-0.09” from MOS. Raw model (from TAMU website): 0.00”

GFS MOS forecast for Flagstaff

Question 1(f): GFS precipitation forecast (not MOS)

Flagstaff: decoding METAR for forecast verification

• Look for 6-hourly high and low temperatures via 5-digit codes that begin with “1” and “2”.

• Look for the highest wind speed value every hour (verification can be different)

• Look for the precipitation accumulated every 6 hours (purple)

06 UTC – 12 UTC Fri 30th  MIN 13.3C = 56F.0.11” OF RAIN KFLG 301157Z AUTO 00000KT 10SM CLR 13/13 A3039 RMK AO2 SLP197 60011 70095 T01330128 10144 20133 55005 TSNO

KFLG 301057Z AUTO 21004KT 10SM FEW080 14/13 A3038 RMK AO2 SLP193 T01390133 TSNO

KFLG 300957Z AUTO 00000KT 10SM BKN090 14/13 A3040 RMK AO2 SLP205 T01440133 TSNO

KFLG 300857Z AUTO 00000KT 10SM OVC100 14/13 A3041 RMK AO2 RAE55 SLP211 P0001 60011 T01440133 58008 TSNO

KFLG 300757Z AUTO 00000KT 10SM -RA OVC100 14/13 A3043 RMK AO2 SLP208 P0006 T01440133 TSNO

KFLG 300657Z AUTO 00000KT 6SM -RA BR FEW047 OVC085 14/13 A3043 RMK AO2 SLP208 P0004 T01390133 402390111 TSNO

12 UTC – 18 UTC Fri 30th

UNUSUAL PROBLEM: MISSING PRECIPITATION AMOUNT AT 18Z (1757Z)MIN 12.2C = 54FNO RAIN

KFLG 301757Z 00000KT 10SM FEW070 OVC090 20/13 A3042 RMK AO2 SLP206 T02000133 10200 20122 50002

KFLG 301657Z 00000KT 10SM OVC075 19/15 A3042 RMK AO2 SLP201 T01940150

KFLG 301557Z 00000KT 10SM BKN090 BKN100 17/14 A3042 RMK AO2 SLP205 T01720144

KFLG 301457Z 00000KT 10SM OVC095 16/14 A3041 RMK AO2 SLP208 T01560139 51005

KFLG 301357Z 00000KT 10SM BKN085 13/12 A3041 RMK AO2 SLP209 T01330122

(13Z observation missing)

18 UTC Fri 30th – 00 UTC Sat 31st

MAX 23.3C = 74F0.32” OF RAIN (IN AN HOUR!) KFLG 302357Z 15003KT 10SM RA FEW042 SCT070 OVC085 18/16 A3034 RMK AO2 RAB18 SLP186 P0032 60032 T01780156 10233 20172 55008

KFLG 302257Z 28006KT 10SM BKN038 OVC060 21/14 A3033 RMK AO2 SLP173 T02110139

KFLG 302157Z 36006KT 10SM FEW035 SCT047 SCT100 22/13 A3035 RMK AO2 SLP175 T02220128

KFLG 302057Z 28007KT 240V300 10SM SCT090 21/14 A3037 RMK AO2 SLP187 T02110144 57013

KFLG 301957Z 21010KT 10SM BKN033 BKN042 OVC070 20/15 A3039 RMK AO2 SLP195 T02000150

KFLG 301857Z 02006KT 10SM FEW055 22/13 A3040 RMK AO2 SLP195 T02220133

00 UTC – 06 UTC Sat 31st

0.07” OF RAIN

KFLG 310557Z AUTO 24003KT 10SM FEW012 BKN090 OVC120 16/15 A3036 RMK AO2 SLP184 60007 T01560150 10178 20156 50002 TSNO

KFLG 310457Z AUTO 24005KT 1/4SM FG VV002 16/16 A3037 RMK AO2 SLP185 T01560156 TSNO

KFLG 310357Z 24003KT 7SM BKN004 BKN110 16/16 A3036 RMK AO2 SLP189 T01610156

KFLG 310257Z 23005KT 10SM SCT004 OVC100 16/16 A3036 RMK AO2 SLP189 60007 T01610156 53004

KFLG 310157Z 21006KT 10SM OVC095 17/16 A3035 RMK AO2 RAE52 SLP190 P0001 T01670161

KFLG 310057Z 20007KT 10SM RA OVC090 17/16 A3034 RMK AO2 SLP187 P0006 T01720161

Forecast Verification: Flagstaff

Verification from METAR: 74-54-10-0.50”

Recall GFS MOS prediction: 78-59-4-(0-0.09”)

Raw GFS precipitation forecast = 0.00”

Was the GFS MOS and GFS a good forecast?

NO! A little too warm (day and night), and a hopelessly low forecast of precipitation.

Lab1 – North American Monsoon

http://en.wikipedia.org/wiki/File:Monsoonmapb.JPG

• Most active within June – August, decays in September and October

Desert heat low, surface trough

Moisture advected due to ocean high

http://www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php

Plotting METAR data: Station Modelshttp://www.rap.ucar.edu/weather/surface/

Mean sea level pressure in mb/10, with first “9” or “10” removed.

1000.5 mb here

http://www.rap.ucar.edu/weather/info/index.php?referrer=surface

Map of Station Models

Miami:12:13pm on Sep 3rd Temp: 89°F, Dew: 74°FPres: 1016.8 mbWind: SE @ 5ktSky: Broken Clouds

How is wind

related to pressure?

Surface analysis based on Station Models

Winds: No FrictionWinds, in the absence of any

frictional forces, are the result of a balance of forces acting on a parcel of air:

• Pressure Gradient Force

-(1/r)*(dP/dx)

• Coriolis Force

2*W*sin(latitude)*(velocity)

• Net wind blows parallel to lines of constant height or pressure, with lower values on to the left of the wind directionHIGH

LOWPGF

CORIOLIS

WIND

Upper tropospheric WindsWinds blow parallel to lines of constant height or pressure

The tighter the gradient of pressure, the stronger the wind

The balance of the pressure gradient force and the Coriolis force is called

GEOSTROPHIC BALANCE

Surface Winds

Winds are the net result of forces acting on a parcel of air:

• Pressure Gradient Force

• Coriolis Force

• Friction – Caused by the surface roughness

996 mb

1000 mb

1004 mb

1008 mb

1012 mb

HIGH

LOW

WIND

PGF

CORIOLIS

FRICTION

Surface Winds Surface winds spiral into and counter clockwise around a low pressure center

Surface winds spiral out from and clockwise around a high pressure center

http://www.rap.ucar.edu/weather/model/