NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260814_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 08/14 18Z 2.20 3310  82  58   9 0.00
Fri 08/14 19Z 1.88 3211  78  64   9 0.00
Fri 08/14 20Z 1.29 3211  77  68  10 0.00
Fri 08/14 21Z 1.19 3212  78  65  10 0.00
Fri 08/14 22Z 0.57 3211  80  56  10 0.00
Fri 08/14 23Z 0.44 3213  81  57  10 0.01
Sat 08/15 00Z 0.46 3216  81  53   9 0.01
Sat 08/15 01Z 0.35 3317  81  42   9 0.00
Sat 08/15 02Z 0.29 3417  83  33   9 0.00
Sat 08/15 03Z 0.23 3416  82  27   9 0.00
Sat 08/15 04Z 0.20 3415  83  23   8 0.00
Sat 08/15 05Z 0.14 3412  82  20   8 0.00
Sat 08/15 06Z 0.12 3410  81  16   8 0.00
Sat 08/15 07Z 0.20 3309  80  15   8 0.00
Sat 08/15 08Z 0.25 3210  78  12   8 0.00
Sat 08/15 09Z 0.34 3211  79  10   8 0.00
Sat 08/15 10Z 0.40 3113  80  10   7 0.00
Sat 08/15 11Z 0.43 3114  81   9   7 0.00
Sat 08/15 12Z 0.36 3215  83  10   7 0.00
Sat 08/15 13Z 0.29 3214  84  11   7 0.00
Sat 08/15 14Z 0.24 3313  83  12   7 0.00
Sat 08/15 15Z 0.23 3311  81  13   8 0.00
Sat 08/15 16Z 0.23 3210  80  14   8 0.00
Sat 08/15 17Z 0.28 3210  80  13   8 0.00
Sat 08/15 18Z 0.38 3211  78  12   8 0.00
Sat 08/15 19Z 0.55 3211  74  11   8 0.00
Sat 08/15 20Z 0.76 3311  73  10   8 0.00
Sat 08/15 21Z 0.32 3209  72   9   9 0.00
Sat 08/15 22Z 0.17 3309  68   9   9 0.00
Sat 08/15 23Z 0.10 3409  64   9   9 0.00
Sun 08/16 00Z 0.09 3409  61  10   9 0.00
Sun 08/16 01Z 0.08 3408  59  10   9 0.00
Sun 08/16 02Z 0.10 3308  59  10   9 0.00
Sun 08/16 03Z 0.09 3409  59  11   9 0.00
Sun 08/16 04Z 0.05 3407  59  12  10 0.00
Sun 08/16 05Z 0.03 3404  55  11  10 0.00
Sun 08/16 06Z 0.05 3204  55  10  10 0.00
Sun 08/16 07Z 0.03 3302  53   8  11 0.00
Sun 08/16 08Z 0.02 2900  51   9  11 0.00
Sun 08/16 09Z 0.03 2002  53   9  11 0.00
Sun 08/16 10Z 0.07 2104  56  10  10 0.00
Sun 08/16 11Z 0.06 2005  57  11  10 0.00
Sun 08/16 12Z 0.14 2108  65  10   9 0.00
Sun 08/16 13Z 0.19 2110  72  10   9 0.00
Sun 08/16 14Z 0.21 2112  75  10   9 0.00
Sun 08/16 15Z 0.26 2212  78   8   9 0.00
Sun 08/16 16Z 0.28 2211  81   6  10 0.00
Sun 08/16 17Z 0.24 2109  81   5  10 0.00
Sun 08/16 18Z 0.22 2009  81   6  10 0.00
Sun 08/16 19Z 0.16 1910  83   6  11 0.00
Sun 08/16 20Z 0.17 1911  86  16  11 0.00
Sun 08/16 21Z 0.15 1912  87  23  11 0.00
Sun 08/16 22Z 0.13 1914  89  30  11 0.00
Sun 08/16 23Z 0.21 1917  90  41  11 0.00
Mon 08/17 00Z 0.27 2019  93  50  12 0.00
Mon 08/17 01Z 0.26 2021  94  86  12 0.01
Mon 08/17 02Z 0.30 2025  96  81  12 0.02
Mon 08/17 03Z 0.38 2027  98  81  13 0.04
Mon 08/17 04Z 0.46 2127  97  89  13 0.03
Mon 08/17 05Z 0.48 2129  97  91  13 0.02

Run total areal avg QPF for the greens is: 0.14 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