NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260815_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 08/15 18Z 0.85 3208  87  28   9 0.00
Sat 08/15 19Z 0.43 3310  81  21   9 0.01
Sat 08/15 20Z 0.19 3411  75  19  10 0.01
Sat 08/15 21Z 0.16 3510  73  16  10 0.00
Sat 08/15 22Z 0.15 3509  76  12   9 0.00
Sat 08/15 23Z 0.15 3510  77   9   9 0.00
Sun 08/16 00Z 0.17 0010  76   9   9 0.00
Sun 08/16 01Z 0.16 0110  74   9   9 0.00
Sun 08/16 02Z 0.16 0208  70   9  10 0.00
Sun 08/16 03Z 0.12 0305  65  10  10 0.00
Sun 08/16 04Z 0.06 0502  63  12  10 0.00
Sun 08/16 05Z 0.03 1300  62  13  10 0.00
Sun 08/16 06Z 0.03 1901  61  14  10 0.00
Sun 08/16 07Z 0.04 2201  60  14  10 0.00
Sun 08/16 08Z 0.06 2302  60  13  10 0.00
Sun 08/16 09Z 0.06 2102  60  11  10 0.00
Sun 08/16 10Z 0.10 2104  62  10  10 0.00
Sun 08/16 11Z 0.10 2203  65   9  10 0.00
Sun 08/16 12Z 0.10 2005  69   7   9 0.00
Sun 08/16 13Z 0.13 2006  73   7   9 0.00
Sun 08/16 14Z 0.17 2007  77   6   9 0.00
Sun 08/16 15Z 0.27 2007  80   6   9 0.00
Sun 08/16 16Z 0.33 1907  82   6  10 0.00
Sun 08/16 17Z 0.30 1807  83   6  10 0.00
Sun 08/16 18Z 0.26 1809  84   6  11 0.00
Sun 08/16 19Z 0.20 1811  85   6  11 0.00
Sun 08/16 20Z 0.23 1812  86   5  11 0.00
Sun 08/16 21Z 0.25 1913  90   4  12 0.00
Sun 08/16 22Z 0.27 1914  98  21  12 0.01
Sun 08/16 23Z 0.31 2017  98  40  12 0.02
Mon 08/17 00Z 0.36 2019  97  50  12 0.01
Mon 08/17 01Z 0.36 2021  98  75  12 0.02
Mon 08/17 02Z 0.42 2024  98  82  12 0.03
Mon 08/17 03Z 0.45 2027  97  88  13 0.01
Mon 08/17 04Z 0.47 2027  97  94  13 0.01
Mon 08/17 05Z 0.45 2027  98  95  13 0.01
Mon 08/17 06Z 0.42 2025  98  95  13 0.01
Mon 08/17 07Z 0.41 2026  98  93  13 0.02
Mon 08/17 08Z 0.42 2026  99  94  12 0.02
Mon 08/17 09Z 0.45 2025  98  96  12 0.03
Mon 08/17 10Z 0.45 2026  98  89  12 0.02
Mon 08/17 11Z 0.41 2023  98  90  12 0.02
Mon 08/17 12Z 0.38 2021  99  87  13 0.02
Mon 08/17 13Z 0.36 2020  99  90  13 0.02
Mon 08/17 14Z 0.35 2119  99  91  13 0.02
Mon 08/17 15Z 0.32 2117  99  90  14 0.02
Mon 08/17 16Z 0.30 2116  99  93  14 0.01
Mon 08/17 17Z 0.27 2113  99  90  14 0.01
Mon 08/17 18Z 0.23 2210  99  87  14 0.01
Mon 08/17 19Z 0.20 2208  99  90  14 0.00
Mon 08/17 20Z 0.18 2406  99  88  14 0.00
Mon 08/17 21Z 0.16 2705  99  87  14 0.00
Mon 08/17 22Z 0.13 3005  99  88  14 0.01
Mon 08/17 23Z 0.12 3107  99  85  14 0.00
Tue 08/18 00Z 0.08 3308  99  61  14 0.00
Tue 08/18 01Z 0.08 3309  98  36  14 0.00
Tue 08/18 02Z 0.07 3310  96  34  13 0.00
Tue 08/18 03Z 0.03 3411  95  24  13 0.00
Tue 08/18 04Z 0.04 3412  96  12  13 0.01
Tue 08/18 05Z 0.03 3412  96   6  13 0.01

Run total areal avg QPF for the Central_Greens is: 0.40 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1