IFR Study 081209 IFR Ceilings Joe Nield Your

IFR Study – 08/12/09 IFR Ceilings Joe Nield – Your Friendly Neighborhood 08/11/09 Evening Shift Aviation Forecaster

Setting the Stage • Isolated to scattered late afternoon/evening thunderstorms improve setting for IFR with HUF/IND both receiving some rainfall. (Radar image from near 00 z 8/12)

Synoptic Situation – 00 Z

Synoptic Situation – 03 Z

Synoptic Situation – 06 Z

Synoptic Situation – 09 Z

Synopsis • Slowly departing cold/quasistationary front (12 z sfc not shown due to extreme movement of boundary between 09 -12 z – appeared unreasonable) • Slowly weakening secondary trough/troughs • Advancing surface high with light northerly/northwesterly flow ahead

What Was Forecast? 000 FTUS 43 KIND 112300 TAFIND TAF KIND 112320 Z 1200/1306 33007 KT P 6 SM FEW 040 SCT 140 FM 120900 36004 KT 3 SM BR SKC FM 121300 01005 KT P 6 SM FEW 250 FM 121700 35008 KT P 6 SM SCT 040 FM 130000 03005 KT P 6 SM SKC= 000 FTUS 43 KIND 112300 TAFLAF TAF KLAF 112320 Z 1200/1224 36009 KT P 6 SM SKC FM 120700 36003 KT 5 SM BR SKC FM 121000 00000 KT 2 SM BR SKC FM 121300 03005 KT P 6 SM SKC FM 121700 01007 KT P 6 SM FEW 040 AMD LTD TO CLD VIS AND WIND 1201/1213= 000 FTUS 43 KIND 112300 TAFHUF TAF KHUF 112320 Z 1200/1224 30004 KT P 6 SM FEW 040 FM 120500 34003 KT 4 SM BR SKC FM 120900 00000 KT 1 SM BR SKC FM 121300 01005 KT P 6 SM SKC FM 121700 36006 KT P 6 SM SCT 040= 000 FTUS 43 KIND 112300 TAFBMG TAF KBMG 112320 Z 1200/1224 33004 KT P 6 SM FEW 040 FM 120500 33003 KT 4 SM BR SKC FM 120900 00000 KT 1 SM BR SKC FM 121300 02005 KT P 6 SM SKC FM 121700 36006 KT P 6 SM SCT 040 AMD LTD TO CLD VIS AND WIND 1201/1213=

Why Was It Forecast? AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE INDIANAPOLIS IN 710 PM EDT TUE AUG 11 2009. AVIATION. . . DISCUSSION FOR THE 00 Z TAFS. IMPACT FOR THIS TAF PKG WL BE PSBL IFR FOG OVRNGT. 18 Z MOS APPEARS TO BE HANDLING SFC DEWPOINT SITUATION MUCH BETTER THAN 12 Z DID. . . AND ALL SITES SAVE FOR IND ARE SHOWN WITH IFR FOG LATE TNGT. BOTH HUF AND IND HAVE SEEN SOME LIGHT RAIN LATE THIS AFTN TO SET THE STAGE EVEN FURTHER. W/ SFC HIGH MOVING IN BEHIND SECONDARY TROUGH SWINGING THROUGH. . . AND DRIEST DEWPOINTS SLOW TO FOLLOW. . . SIGNIFICANT RADIATION INVERSION SHOULD SET UP TNGT W/ DRY AIR ALOFT. . . MORE THAN ADEQUATE CONDITIONS FOR IFR FOG FORMATION AND MAINTENANCE. FOG WL FOLLOW TYPICAL DIURNAL CYCLE. . . BURNING OFF AROUND 13 Z. . . AND TMRW WL BE QUIET W/ ONLY FEW-SCT 040 AFTN CU.

How about at 06 Z? 000 FTUS 43 KIND 120500 TAFIND TAF KIND 120520 Z 1206/1312 01006 KT P 6 SM FEW 100 FM 120900 36004 KT 3 SM BR SKC FM 121300 01005 KT P 6 SM FEW 250 FM 121700 35008 KT P 6 SM SCT 040 FM 130000 03005 KT P 6 SM SKC= 000 FTUS 43 KIND 120500 TAFLAF TAF KLAF 120520 Z 1206/1306 01003 KT P 6 SM SKC FM 120800 36003 KT 5 SM BR SKC TEMPO 1210/1212 2 SM BR FM 121300 03005 KT P 6 SM SKC FM 121700 01007 KT P 6 SM FEW 040 AMD LTD TO CLD VIS AND WIND 1201/1213= 000 FTUS 43 KIND 120500 TAFHUF TAF KHUF 120520 Z 1206/1306 36003 KT P 6 SM FEW 100 FM 120800 35002 KT 4 SM BR SKC FM 121000 00000 KT 2 SM BR SKC FM 121300 01005 KT P 6 SM SKC FM 121700 36006 KT P 6 SM SCT 040= 000 FTUS 43 KIND 120500 TAFBMG TAF KBMG 120520 Z 1206/1306 36003 KT P 6 SM SCT 100 FM 120800 00000 KT 4 SM BR SKC FM 121000 00000 KT 1 SM BR SKC FM 121300 02005 KT P 6 SM SKC FM 121700 36006 KT P 6 SM SCT 040 AMD LTD TO CLD VIS AND WIND 1201/1213=

Still Similar – Minor Changes AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE INDIANAPOLIS IN 1258 AM EDT WED AUG 12 2009 . AVIATION. . . DISCUSSION FOR THE 12/0600 Z TAFS. IMPACT FOR THIS TAF PKG WL BE PSBL IFR FOG TNGT. 00 Z MOS NO LONGER SHOWING IFR CONDS LIKE THE 18 Z MOS GUIDANCE. . . BUT THE SETUP IS STILL THERE FOR IFR TO FORM AS A SIGNIFICANT RADIATION INVERSION SETS UP OVERNIGHT. RUC 13 MODEL ALSO HINTS AT IFR FOG AS WELL. DRIER AIR IS TRYING TO WORK INTO LAF BUT REMAINDER OF SITES STILL HAVE LOW 60 S DEWPOINTS. WITH NO STRONG PUSH OF DRY AIR. . . AND THE FACT THAT SOME RAIN FELL AT HUF/IND EARLIER. . . WILL CONTINUE PREV FORECAST OF IFR FOG FOR A PERIOD AT ALL SITES BUT IND. FOG WL FOLLOW TYPICAL DIURNAL CYCLE. . . BURNING OFF AROUND 13 Z. . . AND TMRW WL BE QUIET W/ ONLY FEW-SCT 040 AFTN CU.

More on Why (No, not moron, why? !) • I expected, based on guidance winds/vsby progs and relative tendencies at IND, that best conditions would be at IND, with lower conditions at LAF, and even lower at HUF/BMG where rainfall had occurred that evening. • Afternoon/evening BUFKIT data, which I regrettably failed to have archived (06 z/12 z runs 08/12 were archived and are similar), depicted a shallow but still significant surface moist layer below a strong radiation inversion with dry air aloft. This layer was less shallow on the 18 z BUFKIT data than on the archived examples shown next • BUFKIT fog progs (MRi) did hint that stratus might have been favored over fog, but weak MOS winds drew me back to fog

IND BUFKIT Profile

IND BUFKIT Profile (zoomed)

LAF BUFKIT Profile

LAF BUFKIT Profile (zoomed)

What Happened? 08/12/09 05: 54: 25 METAR KIND 121054 Z 34007 KT 10 SM CLR 16/14 A 3004 RMK AO 2 SLP 167 T 01610144 (CMK) 08/12/09 06: 53: 21 SPECI KIND 121152 Z 33005 KT 10 SM BKN 006 17/15 A 3005 RMK AO 2 FIBI (MAB) 08/12/09 07: 08: 25 SPECI KIND 121208 Z 33006 KT 10 SM BKN 006 17/15 A 3006 RMK AO 2 (MAB) 08/12/09 07: 54: 25 METAR KIND 121254 Z 36008 KT 10 SM BKN 006 19/16 A 3006 RMK AO 2 SLP 175 T 01890156 (MAB) 08/12/09 08: 12: 25 SPECI KIND 121312 Z 36005 KT 10 SM SCT 006 19/16 A 3007 RMK AO 2 (MAB) 08/12/09 08: 54: 25 METAR KIND 121354 Z 01006 KT 10 SM SCT 006 21/17 A 3007 RMK AO 2 SLP 179 T 02060167 (MAB) • LAF followed a similar pattern, getting down to BKN 003. IFR lasted for a shorter period of time at LAF. HUF experienced brief MVFR (BKN 012) ceilings, and BMG remained clear.

What went (sort of) right? • Looking at it through the new Categorical Amendment Criteria, IFR was in the forecast at LAF/HUF/BMG, and low end MVFR was forecast at IND – so it didn’t go entirely undetected, although significant false alarms occurred at HUF/BMG, and to a lesser extent, LAF – and IND was a missed event.

What went wrong? • Obviously, low stratus occurred rather than fog. All sites but LAF remained unrestricted at the surface, with LAF dropping to 4 SM and coming back up as IFR conditions ended.

What made the difference? • Winds only briefly went calm at most locations – never calm at IND. Winds were generally 4 -7 knots throughout the night. • Surface moist layer was perhaps too shallow to support fog development • Recalling BUFKIT profiles shown earlier – with encroaching high pressure, subsidence is seen throughout MOST of the column – but weak lift is present in the lower levels. (Left over from decaying secondary trough/troughs perhaps? ) This along with the lack of calm surface winds likely contributed to a lifting of the near surface moisture into a brief low stratus layer near and just after sunrise

Thanks for viewing! I might have gone down, but at least I went down trying!