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 Thursdays Lab Surface Station Models Pressure-Wind Relationship

Surface Weather Analysis

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

ASOS: 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 °F

METAR Observations Example METAR Report METAR KABC Z 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 T TSNO $ KABC - ICAO STATION (location) IDENTIFIER Four character ICAO location identifier Z - 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.

METAR Observations Example METAR Report METAR KABC Z 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 T 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 60 o 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 Z 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 T 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 Z 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 T 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) 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. 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 Z 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 T 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 Z 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 T 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 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 Z 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 T TSNO $ P 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) 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 (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., indicates 0.15 inches of precipitation for past 24 hours.

METAR Observations Example METAR Report METAR KABC Z 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 T TSNO $ T HOURLY TEMPERATURE AND DEW POINT. TsnTaTaTa snT'aT'aT'a; reported to nearest tenth of o C; sn: 1 if temperature or dew point below 0 o C and 0 if temperature/dew point 0 o C or higher. (+6.4C / +3.6C here) 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 0 o C and 0 if temperature 0 o C or higher (max of +6.6C in past 6h here) 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 0 o C and 0 if temperature 0 o C or higher. (min of -1.2C in past 6h here) 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 0 o C and 0 if temperature 0 o C 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 F Min Temp 59 F Max Wind Speed 4 kt Precipitation amount: 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 30 th MIN 13.3C = 56F OF RAIN KFLG Z AUTO 00000KT 10SM CLR 13/13 A3039 RMK AO2 SLP T TSNO KFLG Z AUTO 21004KT 10SM FEW080 14/13 A3038 RMK AO2 SLP193 T TSNO KFLG Z AUTO 00000KT 10SM BKN090 14/13 A3040 RMK AO2 SLP205 T TSNO KFLG Z AUTO 00000KT 10SM OVC100 14/13 A3041 RMK AO2 RAE55 SLP211 P T TSNO KFLG Z AUTO 00000KT 10SM -RA OVC100 14/13 A3043 RMK AO2 SLP208 P0006 T TSNO KFLG Z AUTO 00000KT 6SM -RA BR FEW047 OVC085 14/13 A3043 RMK AO2 SLP208 P0004 T TSNO

12 UTC – 18 UTC Fri 30 th UNUSUAL PROBLEM: MISSING PRECIPITATION AMOUNT AT 18Z (1757Z) MIN 12.2C = 54F NO RAIN KFLG Z 00000KT 10SM FEW070 OVC090 20/13 A3042 RMK AO2 SLP206 T KFLG Z 00000KT 10SM OVC075 19/15 A3042 RMK AO2 SLP201 T KFLG Z 00000KT 10SM BKN090 BKN100 17/14 A3042 RMK AO2 SLP205 T KFLG Z 00000KT 10SM OVC095 16/14 A3041 RMK AO2 SLP208 T KFLG Z 00000KT 10SM BKN085 13/12 A3041 RMK AO2 SLP209 T (13Z observation missing)

18 UTC Fri 30 th – 00 UTC Sat 31 st MAX 23.3C = 74F 0.32 OF RAIN (IN AN HOUR!) KFLG Z 15003KT 10SM RA FEW042 SCT070 OVC085 18/16 A3034 RMK AO2 RAB18 SLP186 P T KFLG Z 28006KT 10SM BKN038 OVC060 21/14 A3033 RMK AO2 SLP173 T KFLG Z 36006KT 10SM FEW035 SCT047 SCT100 22/13 A3035 RMK AO2 SLP175 T KFLG Z 28007KT 240V300 10SM SCT090 21/14 A3037 RMK AO2 SLP187 T KFLG Z 21010KT 10SM BKN033 BKN042 OVC070 20/15 A3039 RMK AO2 SLP195 T KFLG Z 02006KT 10SM FEW055 22/13 A3040 RMK AO2 SLP195 T

00 UTC – 06 UTC Sat 31 st 0.07 OF RAIN KFLG Z AUTO 24003KT 10SM FEW012 BKN090 OVC120 16/15 A3036 RMK AO2 SLP T TSNO KFLG Z AUTO 24005KT 1/4SM FG VV002 16/16 A3037 RMK AO2 SLP185 T TSNO KFLG Z 24003KT 7SM BKN004 BKN110 16/16 A3036 RMK AO2 SLP189 T KFLG Z 23005KT 10SM SCT004 OVC100 16/16 A3036 RMK AO2 SLP T KFLG Z 21006KT 10SM OVC095 17/16 A3035 RMK AO2 RAE52 SLP190 P0001 T KFLG Z 20007KT 10SM RA OVC090 17/16 A3034 RMK AO2 SLP187 P0006 T

Forecast Verification: Flagstaff Verification from METAR: Recall GFS MOS prediction: (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 Most active within June – August, decays in September and October Desert heat low, surface trough Moisture advected due to ocean high

Plotting METAR data: Station Models Mean sea level pressure in mb/10, with first 9 or 10 removed mb here

Map of Station Models Miami: 12:13pm on Sep 3 rd Temp: 89°F, Dew: 74°F Pres: mb Wind: 5kt Sky: Broken Clouds

How is wind related to pressure? Surface analysis based on Station Models

Winds: No Friction Winds, 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/ )*(dP/dx) Coriolis Force 2* *sin(latitude)*(velocity) Net wind blows parallel to lines of constant height or pressure, with lower values on to the left of the wind direction HIGH LOW PGF CORIOLIS WIND

Upper tropospheric Winds Winds blow parallel to lines of constant height or pressure The tighter the gradient of pressure, the stronger the wind GEOSTROPHIC BALANCE 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