Climatology of Inverted Troughs over the Gulf of Maine Joseph Cebulko, Jason Cordeira, Justin Arnott, and Lance Bosart

Motivation

Base reflectivity (dBZ) Cyclones that contain ITs deviate from traditional cyclone models ITs may produce poorly forecast “surprise” snow events Little previous research

Background

Cool Season Phenomena Weisman et al. 2002

What is an IT? Elongated region of relatively low atmospheric pressure extending north/westward from a parent low over Northwest Atlantic Has ability to focus and lift moisture in an unstable atmosphere resulting intense/persistent snow squalls (Lundstedt 1993)

ITs over the Gulf of Maine 5 Criteria for Significant Snowfall Production (Lundstedt 1993) Surface-to-850-hPa ΔT ≥ 10°C Boundary Layer RH > 50% with wind component from off the ocean on one side of the IT 500-hPa positive AVOR advection observed with 700-hPa UVM Quasi-stationary IT axis for ~6 hours 850-hPa flow is weak OR parallel to surface IT

Data and Methodology

Data and IT Examples North American Regional Reanalysis dataset (NARR) Plotted MSLP at 3-hr intervals Sept-May 1989-2013 Subjective analysis of objectively analyzed reanalysis data Subset data by orientation for composite analyses IT max amplification and study area

Precipitation and ITs United States Unified Precipitation dataset (UPD)

Climatology

Annual Climatology

Monthly Climatology

K-means Clustering k=2

K-means Clustering k=2

K-means Clustering k=2

Two Scenarios NW-SE oriented ITs W-E oriented ITs

Headlines issued on 36 of 57 (~63%) IT precip days 57 of 83 IT days (~69%) (avg ~19 mm) ~8–10 inches Headlines issued on 36 of 57 (~63%) IT precip days

Climatology Summary Data suggest that ITs are cool season phenomena Majority of IT-influenced precipitation impacts the central Maine coast Precipitation (~19 mm) observed on ~69% of days with an IT Majority of ITs with precipitation are headlined (~63%) Data suggests High-Impact Sub-Advisory (HISA) characteristic of ITs

Composite Life Cycle

t − 12 h 500-hPa Heights/Winds/AVOR 700-hPa Heights/Winds/UVM (×10−5 s−1; shaded according to scale) (hPa s−1; shaded according to scale) MSLP & 10-m winds/divergence (s−1; shaded according to scale)

t − 12 h 850-hPa Heights/Temps/Q-Vectors/QDIV 950-hPa Heights/Winds/Temps/FGEN [shaded; K (100 km)−1 3 h−1] MSLP & 10-m winds/divergence (s−1; shaded according to scale)

t − 0 h 500-hPa Heights/Winds/AVOR 700-hPa Heights/Winds/UVM (×10−5 s−1; shaded according to scale) (hPa s−1; shaded according to scale) MSLP & 10-m winds/divergence (s−1; shaded according to scale)

t − 0 h 850-hPa Heights/Temps/Q-Vectors/QDIV 950-hPa Heights/Winds/Temps/FGEN [shaded; K (100 km)−1 3 h−1] MSLP & 10-m winds/divergence (s−1; shaded according to scale)

t + 12 h 500-hPa Heights/Winds/AVOR 700-hPa Heights/Winds/UVM (×10−5 s−1; shaded according to scale) (hPa s−1; shaded according to scale) MSLP & 10-m winds/divergence (s−1; shaded according to scale)

t + 12 h 850-hPa Heights/Temps/Q-Vectors/QDIV 950-hPa Heights/Winds/Temps/FGEN [shaded; K (100 km)−1 3 h−1] MSLP & 10-m winds/divergence (s−1; shaded according to scale)

Composite Analysis: Summary Robust forcing for UVM extending away from parent low, confirmed by Q-Vector convergence Frontogenesis ≥ 4 K (100 km)−1 3 h−1 within IT Speed and directional wind convergence along IT axis Life cycle requires < 24 h for completion

Operational Implications

Concluding Remarks This study created a climatology of ITs over Gulf of Maine Synoptic-scale processes lead to development/orientation of ITs Mesoscale processes influence IT precipitation (headline vs no- headline) New England WFOs will be able utilize this research in operational applications Plethora of avenues for future work Thank you! joseph.cebulko@noaa.gov