NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260430_0000
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)
=== ===== === ==== ==== === === === ====
Thu 04/30 00Z 0.23 1520  70  87   6 0.00
Thu 04/30 01Z 0.13 1522  71  85   7 0.00
Thu 04/30 02Z 0.07 1623  72  81   7 0.00
Thu 04/30 03Z 0.05 1625  73  81   7 0.00
Thu 04/30 04Z 0.03 1626  68  78   8 0.00
Thu 04/30 05Z 0.13 1825  74  84   6 0.00
Thu 04/30 06Z 0.12 1824  76  83   5 0.00
Thu 04/30 07Z 0.13 1825  85  96   4 0.01
Thu 04/30 08Z 0.14 1823  96  98   5 0.07
Thu 04/30 09Z 0.17 1823  97  99   3 0.07
Thu 04/30 10Z 0.21 1921  96  98   3 0.02
Thu 04/30 11Z 0.20 2016  97  99   3 0.02
Thu 04/30 12Z 0.17 2012  97  94   3 0.01
Thu 04/30 13Z 0.17 2010  97  95   3 0.01
Thu 04/30 14Z 0.17 2110  98  96   3 0.02
Thu 04/30 15Z 0.18 2108  98  96   3 0.01
Thu 04/30 16Z 0.18 2107  99  97   2 0.02
Thu 04/30 17Z 0.20 2207 100  97   1 0.02
Thu 04/30 18Z 0.24 2306 100  93   1 0.03
Thu 04/30 19Z 0.28 2606 100  86   1 0.03
Thu 04/30 20Z 0.31 2908 100  90   1 0.03
Thu 04/30 21Z 0.28 3111  99  96   0 0.03
Thu 04/30 22Z 0.28 3114  98  93   0 0.01
Thu 04/30 23Z 0.34 3115  94  82   0 0.01
Fri 05/01 00Z 0.40 3117  91  65   0 0.00
Fri 05/01 01Z 0.47 3118  94  62   0 0.00
Fri 05/01 02Z 0.50 3017  95  64  -1 0.00
Fri 05/01 03Z 0.53 3017  95  53  -1 0.00
Fri 05/01 04Z 0.53 3018  96  47  -1 0.01
Fri 05/01 05Z 0.53 3118  96  46  -2 0.01
Fri 05/01 06Z 0.53 3118  95  40  -2 0.01
Fri 05/01 07Z 0.53 3018  94  40  -2 0.00
Fri 05/01 08Z 0.52 3018  93  42  -2 0.00
Fri 05/01 09Z 0.51 3017  92  47  -3 0.00
Fri 05/01 10Z 0.52 3017  92  48  -3 0.00
Fri 05/01 11Z 0.57 3017  92  48  -3 0.00
Fri 05/01 12Z 0.63 3016  91  45  -3 0.00
Fri 05/01 13Z 1.08 3015  89  50  -3 0.00
Fri 05/01 14Z 3.07 3013  86  49  -3 0.00
Fri 05/01 15Z 5.14 3010  83  56  -3 0.00
Fri 05/01 16Z 5.19 2809  82  68  -2 0.00
Fri 05/01 17Z 5.63 2709  82  53  -2 0.00
Fri 05/01 18Z 5.66 2708  75  40  -1 0.00
Fri 05/01 19Z 5.67 2709  73  45  -1 0.00
Fri 05/01 20Z 5.03 2609  74  42  -1 0.00
Fri 05/01 21Z 5.65 2609  71  47   0 0.00
Fri 05/01 22Z 5.14 2710  71  46  -1 0.00
Fri 05/01 23Z 2.70 2710  70  45  -1 0.00
Sat 05/02 00Z 1.47 2811  69  41  -1 0.00
Sat 05/02 01Z 1.05 2811  69  37  -1 0.00
Sat 05/02 02Z 1.07 2811  69  39  -2 0.00
Sat 05/02 03Z 0.86 2911  70  40  -2 0.00
Sat 05/02 04Z 0.63 2910  71  39  -2 0.00
Sat 05/02 05Z 0.44 3008  72  47  -2 0.00
Sat 05/02 06Z 0.32 3006  72  53  -2 0.00
Sat 05/02 07Z 0.32 2805  73  64  -2 0.00
Sat 05/02 08Z 0.27 2605  72  64  -3 0.00
Sat 05/02 09Z 0.27 2505  71  66  -3 0.00
Sat 05/02 10Z 0.23 2505  69  70  -3 0.00
Sat 05/02 11Z 0.23 2405  66  68  -3 0.00

Run total areal avg QPF for the Central_Greens is: 0.45 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