NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260205_0000
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)
=== ===== === ==== ==== === === === ====
Thu 02/05 00Z 0.45 3016  82  35 -12 0.00
Thu 02/05 01Z 0.39 3118  81  34 -12 0.00
Thu 02/05 02Z 0.39 3018  85  36 -12 0.00
Thu 02/05 03Z 0.38 3017  86  37 -12 0.00
Thu 02/05 04Z 0.35 3016  86  39 -12 0.00
Thu 02/05 05Z 0.39 2917  86  41 -12 0.00
Thu 02/05 06Z 0.42 2918  88  39 -13 0.00
Thu 02/05 07Z 0.45 2918  88  42 -13 0.00
Thu 02/05 08Z 0.49 2919  86  50 -13 0.00
Thu 02/05 09Z 0.52 2920  86  56 -14 0.01
Thu 02/05 10Z 0.52 2920  86  67 -14 0.01
Thu 02/05 11Z 0.51 2920  88  78 -15 0.00
Thu 02/05 12Z 0.51 3020  89  52 -15 0.00
Thu 02/05 13Z 0.47 3020  87   9 -16 0.00
Thu 02/05 14Z 0.40 3119  83   2 -16 0.00
Thu 02/05 15Z 0.35 3118  81   2 -16 0.00
Thu 02/05 16Z 0.33 3117  80   2 -16 0.00
Thu 02/05 17Z 0.30 3115  77   3 -16 0.00
Thu 02/05 18Z 0.27 3113  74   3 -16 0.00
Thu 02/05 19Z 0.25 3112  69   4 -15 0.00
Thu 02/05 20Z 0.21 3112  63   3 -14 0.00
Thu 02/05 21Z 0.19 3112  59   3 -14 0.00
Thu 02/05 22Z 0.18 3112  55   3 -13 0.00
Thu 02/05 23Z 0.15 3212  52   4 -12 0.00
Fri 02/06 00Z 0.11 3210  50   4 -12 0.00
Fri 02/06 01Z 0.11 3210  50   5 -12 0.00
Fri 02/06 02Z 0.08 3309  46   6 -12 0.00
Fri 02/06 03Z 0.04 3407  40   7 -11 0.00
Fri 02/06 04Z 0.03 3405  36   8 -11 0.00
Fri 02/06 05Z 0.02 3403  34  10 -10 0.00
Fri 02/06 06Z 0.02 3302  32  11 -10 0.00
Fri 02/06 07Z 0.01 3000  31  10 -10 0.00
Fri 02/06 08Z 0.02 2201  30   9 -11 0.00
Fri 02/06 09Z 0.02 2002  28   9 -10 0.00
Fri 02/06 10Z 0.03 2003  27   8 -10 0.00
Fri 02/06 11Z 0.03 2004  26   7 -10 0.00
Fri 02/06 12Z 0.04 2103  26   8 -10 0.00
Fri 02/06 13Z 0.05 2203  26  13 -10 0.00
Fri 02/06 14Z 0.04 2203  29  31 -11 0.00
Fri 02/06 15Z 0.04 2004  34  50 -11 0.00
Fri 02/06 16Z 0.06 2104  38  67 -11 0.00
Fri 02/06 17Z 0.07 2104  41  79 -11 0.00
Fri 02/06 18Z 0.06 2104  44  85 -11 0.00
Fri 02/06 19Z 0.07 2004  49  87 -11 0.00
Fri 02/06 20Z 0.11 2104  54  87 -11 0.00
Fri 02/06 21Z 0.13 2205  57  87 -12 0.00
Fri 02/06 22Z 0.14 2205  57  87 -12 0.00
Fri 02/06 23Z 0.15 2206  52  89 -12 0.00
Sat 02/07 00Z 0.16 2207  52  90 -11 0.00
Sat 02/07 01Z 0.17 2307  55  88 -12 0.00
Sat 02/07 02Z 0.20 2308  64  88 -12 0.00
Sat 02/07 03Z 0.20 2208  79  88 -12 0.00
Sat 02/07 04Z 0.14 2206  87  88 -12 0.00
Sat 02/07 05Z 0.12 2205  89  87 -12 0.01
Sat 02/07 06Z 0.13 2404  90  87 -12 0.01
Sat 02/07 07Z 0.15 2604  90  85 -12 0.01
Sat 02/07 08Z 0.16 2905  91  87 -13 0.01
Sat 02/07 09Z 0.16 3106  91  85 -13 0.01
Sat 02/07 10Z 0.21 3210  90  83 -13 0.02
Sat 02/07 11Z 0.15 3416  90  81 -14 0.02

Run total areal avg QPF for the greens is: 0.11 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