Meteorological Evolution and Model Performance for Fire Threat

Days Over the Northeast U.S.Joe Pollina1,2, Brian A. Colle1, Mike Erickson1

1School of Marine and Atmospheric SciencesStony Brook University – SUNY

2National Weather Service, New York City

andand Joseph Charney

USDA Forest Service, East Lansing, MI1995 “Sunrise Fire”Westhampton, NYImage taken from the Cutchogue FireDepartment web site at www.cutchoguefiredept.org

1999-Sep 2009 Fire Events (> 100 Acres) Over the Northeast U.S. (excluding PA and ME). 106 events total from the Northeast Interagency Coordination Center

Motivational Questions

• What is climatology of fire-threat days over the Northeast U.S.? No formal studies have been done for the entire Northeast.

• What are the large-scale flow patterns associated with fire threat days across the Northeast, and how do they evolve?

• What are the important physical processes that lead to the fire threat?

• How well do mesoscale models predict these fire threat conditions?

Data and Methods (Climatology)• Data (Jan. 1998-mid Sep. 2009)

– Obtained 97 “fire threat” days which the National Fire Danger Rating System (NFDRS) indicates that the fire danger was “high, very high, or extreme”. This was obtained through the Wildland Fire Assessment System (WFAS) website: http://www.wfas.net/component/option,com_wrapper/Itemid,92/

• Methods– Monthly climatology of Fire Threat Days– Synoptic Flow Classification

• Based on Yarnal (1993)– Large scale flow composite of the “fire threat” days

• Used daily North American Regional Reanalysis (NARR) (Mesinger et al. 2006)

Monthly Climatology of Fire Threat Days

MONTH

PERC

ENTA

GE

Normalized DifferenceVegetation Indexfor 2008 Apr 14

Classification of Synoptic Weather Regimes

• Used Yarnal (1993) classification system that was developed to describe the different types of surface pressure patterns associated with West Virginia fire events.

• Applied 8 different types of weather patterns:– Pre-high (PH)– Back of high (BH)– Extended high (EH)– High pressure cell to the south (HS)– High pressure cell to the north (HN)– Cyclonic conditions with rain (RC)– Cold front passage (CF)– Elongated low (EL)

H

H

H

LH

H

Pre-high Back of high Extended high

H

HL

L

High to the south High to the north

Distribution of Fire Threat Days For Each Yarnal Synoptic Type

PERC

ENTA

GE

YARNAL CLASSIFICATION

PH=pre-highEH=extended highBH=back of highCF=cold frontHS=high to southHN=high to north

Distribution of Synoptic Type By MonthP

erce

ntag

e

Month

Overall:PH: 39.2%EH: 29.9%BH: 20.6%CF: 5.2%HS: 3.1%HN: 2.1%

(pre-high)

(extended high)

(back of high)

(cold front)

(high to the south)

(high to the north)

NARR Composite of All Fire Threat Days

Day of the events24 hours prior to events

48 hours prior toevents

SLP

500Z

Relatively dry and Deep PBL (Well-Mixed) Composite PBL Height (m)

850-mb Relative Humidity (%)

NARR Composite of All Fire Threat Days

Additional Subsidence from TerrainComposite 900 mb Wind Vector Composite 2m RH

NARR Composite of All Fire Threat Days

15-17 April 2008 Overlooks (NY) Fire Event

04/15/12z 04/16/12z 04/17/12z

04/15/12z 04/16/12z 04/17/12z

OverlooksFire

Drying and Warming at Albany, NY (4/14-4/17)

1200 UTC 14 April 2008

Surface RHand wind observationsfor central and southern NY

Origin of the Dry Air Backward trajectory (every 24 h) starting at 12 UTC 17 April 2008 Using Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) program (Draxler and Rolph 2003). Thisshows where the dry airwas 315 hours prior tothe event, and the pathit took up to the time of the event.

4/5 00 UTC

4/6

4/7 4/8

4/9

4/10 4/11

4/12

4/13

4/14

4/15 4/164/17

4/17 12 UTC

4/16 00 UTC

4/17 12 UTC 4/17 12 UTC

4/16 00 UTC

- 10 ETA members at 32 km grid spacing.

- 5 with BMJ CP and Ferrier MP.

- 5 with KF CP and Ferrier MP.

- 5 RSM members at 45 km grid spacing.

- 3 with SAS CP and Zhou GFS MP.

- 2 with RAS CP and Zhou GFS MP.

- 3 WRF-NMM members at 40 km grid spacing.

- 3 WRF-ARW members at 45 km grid spacing.

- IC's are perturbed using a breeding technique.

NCEP SREF 21 Member (21 UTC)

Short-Range Ensemble Systems Stony Brook Univ. 13 Member Ensemble (00 UTC) - 7 MM5, 6 WRFv2.2 members at 12 km grid spacing (NAM soil moisture and SST).

- IC: NAM, GFS, CMC and NOGAPS.

- CP: Grell, KF and Betts-Miller.

- PBL MM5: Blackadar, MRF, MY

- PBL WRF: MYJ and YSU.

- MP MM5: Sice, Reis2

- MP WRF: Ferrier, WSM3.

Verification of surface parameters (e.g.,

2-m temp and 10-m wsp) for 109 NWS

stations over NE for March-Sept 2006-

2009

Surface Temperature Mean Error (12-36h) by Member for Stony Brook and SREF Ensembles

SBU 12-km Ensemble NCEP SREF

(o C)

(o C)

MM5 WRF

MYJ

SREF sub-group averages

Impact of Using Previous 5 Fire Threat Days for Bias Correction of Surface Temperature (12-36 h avg)

SBU 12-km Ensemble NCEP SREF

MM5 WRF

(o C)

(o C)

Note: MAE for SBU+SREF ens mean is 1.84 K (~0.10 K less than best

member, but comparable to SBU mean).

NARR Composite of Top 10 Largest and Smallest Cool Bias on Fire Threat Days

Sea-level

pressure (Pa)

Small T Bias

Small T BiasLarge T Bias

Large T Bias

Cloud Fraction

(%): Cool bias

associated with

partly cloudy

fire threat days

– model too

cloudy??.

Conclusions• Peak fire threat over the Northeast U.S. occurs during the climatological

spring (~52% of events in April). This is the pre green-up period.

• Fire threat days were classified by synoptic type. Pre-high (39%), extended high (30%), and back of high (21%) are the major synoptic patterns associated with a high fire threat.

• NARR composites illustrate high pressure moving south from Canada to the Northeast U.S., with a corresponding ridge at 500 mb approaching the Great Lakes.

• Downsloping from northwesterly flow, subsidence from high pressure, and mixing from large PBL heights are all likely important in bringing in warmer, drier air to the surface.

• Ensembles have relatively large (cool) biases for fire threat days over the Northeast U.S., which are larger than the average warm season biases.

• A standard 14-day bias correction (used by many studies) does not work that well for fire threat days (since weather is more anomalous). A bias correction using last 5 fire threat days removes most of ensemble bias.