NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260917_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 09/17 00Z 0.20 3006  92  18  13 0.00
Thu 09/17 01Z 0.20 3006  91  13  13 0.00
Thu 09/17 02Z 0.18 3107  90  12  13 0.00
Thu 09/17 03Z 0.14 3106  89  12  12 0.00
Thu 09/17 04Z 0.13 3105  90  13  12 0.00
Thu 09/17 05Z 0.11 2904  89  15  12 0.00
Thu 09/17 06Z 0.09 2802  89  19  12 0.00
Thu 09/17 07Z 0.07 2602  87  21  12 0.00
Thu 09/17 08Z 0.07 2203  86  28  12 0.00
Thu 09/17 09Z 0.09 2204  87  35  12 0.00
Thu 09/17 10Z 0.11 2205  90  36  12 0.00
Thu 09/17 11Z 0.14 2206  91  38  12 0.00
Thu 09/17 12Z 0.14 2206  92  37  12 0.00
Thu 09/17 13Z 0.16 2207  93  38  12 0.00
Thu 09/17 14Z 0.17 2208  94  41  12 0.00
Thu 09/17 15Z 0.20 2208  97  43  12 0.00
Thu 09/17 16Z 0.21 2308  98  51  12 0.00
Thu 09/17 17Z 0.20 2308  98  63  12 0.01
Thu 09/17 18Z 0.20 2308  97  73  12 0.01
Thu 09/17 19Z 0.20 2308  98  81  13 0.02
Thu 09/17 20Z 0.22 2408  99  87  13 0.03
Thu 09/17 21Z 0.22 2507  98  92  13 0.04
Thu 09/17 22Z 0.19 2706  95  93  13 0.04
Thu 09/17 23Z 0.18 2806  90  94  13 0.07
Fri 09/18 00Z 0.18 2806  89  94  13 0.05
Fri 09/18 01Z 0.17 2906  87  83  13 0.03
Fri 09/18 02Z 0.19 3007  89  77  13 0.01
Fri 09/18 03Z 0.21 3008  91  81  12 0.01
Fri 09/18 04Z 0.24 3010  91  79  12 0.01
Fri 09/18 05Z 0.27 3011  90  88  12 0.01
Fri 09/18 06Z 0.29 3013  87  81  11 0.01
Fri 09/18 07Z 0.37 3017  87  76  11 0.01
Fri 09/18 08Z 0.38 3119  82  68  10 0.01
Fri 09/18 09Z 0.38 3120  79  64  10 0.01
Fri 09/18 10Z 0.40 3222  78  40   9 0.01
Fri 09/18 11Z 0.48 3225  83  37   8 0.01
Fri 09/18 12Z 0.50 3225  85  21   7 0.01
Fri 09/18 13Z 0.48 3225  83  10   6 0.00
Fri 09/18 14Z 0.50 3324  83  13   6 0.00
Fri 09/18 15Z 0.86 3222  86  10   5 0.00
Fri 09/18 16Z 2.88 3221  83   5   5 0.00
Fri 09/18 17Z 4.70 3220  80   2   5 0.00
Fri 09/18 18Z 3.73 3221  76   2   5 0.00
Fri 09/18 19Z 2.51 3220  70   2   5 0.00
Fri 09/18 20Z 1.75 3220  65   2   4 0.00
Fri 09/18 21Z 0.83 3320  59   2   4 0.00
Fri 09/18 22Z 0.61 3321  54   2   5 0.00
Fri 09/18 23Z 0.37 3321  53   2   5 0.00
Sat 09/19 00Z 0.27 3422  54   3   4 0.00
Sat 09/19 01Z 0.20 3423  55   3   4 0.00
Sat 09/19 02Z 0.12 3423  55   4   4 0.00
Sat 09/19 03Z 0.08 3521  58   5   4 0.00
Sat 09/19 04Z 0.05 3521  57   6   4 0.00
Sat 09/19 05Z 0.04 3519  54   7   4 0.00
Sat 09/19 06Z 0.03 3518  50   7   4 0.00
Sat 09/19 07Z 0.03 3516  45   7   4 0.00
Sat 09/19 08Z 0.03 3515  41   7   4 0.00
Sat 09/19 09Z 0.03 3514  37   7   5 0.00
Sat 09/19 10Z 0.04 3513  35   6   5 0.00
Sat 09/19 11Z 0.03 3513  33   7   5 0.00

Run total areal avg QPF for the greens is: 0.41 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