NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261011_0600
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)
=== ===== === ==== ==== === === === ====
Sun 10/11 06Z 0.14 2109  41  48   9 0.00
Sun 10/11 07Z 0.16 2210  41  48   9 0.00
Sun 10/11 08Z 0.20 2212  42  46  10 0.00
Sun 10/11 09Z 0.19 2113  42  43  10 0.00
Sun 10/11 10Z 0.22 2115  43  42  10 0.00
Sun 10/11 11Z 0.25 2217  44  42  10 0.00
Sun 10/11 12Z 0.29 2219  42  42  11 0.00
Sun 10/11 13Z 0.30 2220  43  42  11 0.00
Sun 10/11 14Z 0.32 2220  45  42  10 0.00
Sun 10/11 15Z 0.31 2219  44  41  10 0.00
Sun 10/11 16Z 0.24 2118  38  42  10 0.00
Sun 10/11 17Z 0.21 2117  37  48  10 0.00
Sun 10/11 18Z 0.17 2017  37  60  10 0.00
Sun 10/11 19Z 0.17 2015  43  78   9 0.00
Sun 10/11 20Z 0.15 2014  50  88   9 0.00
Sun 10/11 21Z 0.15 2015  58  96   8 0.00
Sun 10/11 22Z 0.11 1916  70  96   7 0.00
Sun 10/11 23Z 0.10 1818  79  95   7 0.01
Mon 10/12 00Z 0.11 1819  84  95   7 0.00
Mon 10/12 01Z 0.15 1819  90  94   7 0.01
Mon 10/12 02Z 0.16 1919  95  95   7 0.02
Mon 10/12 03Z 0.19 2016  96  91   7 0.03
Mon 10/12 04Z 0.19 2112  97  87   8 0.05
Mon 10/12 05Z 0.19 2309  97  82   8 0.05
Mon 10/12 06Z 0.19 2707  97  79   8 0.04
Mon 10/12 07Z 0.14 3107  96  73   9 0.03
Mon 10/12 08Z 0.12 3209  94  67   9 0.01
Mon 10/12 09Z 0.13 3311  92  60   9 0.01
Mon 10/12 10Z 0.12 3312  92  53   9 0.00
Mon 10/12 11Z 0.14 3415  91  47   9 0.01
Mon 10/12 12Z 0.12 3415  88  39  10 0.01
Mon 10/12 13Z 0.13 3316  83  36  10 0.01
Mon 10/12 14Z 0.14 3316  80  30  11 0.01
Mon 10/12 15Z 0.13 3315  76  35  12 0.01
Mon 10/12 16Z 0.14 3314  77  43  11 0.00
Mon 10/12 17Z 0.20 3215  80  51  11 0.00
Mon 10/12 18Z 0.25 3116  82  60  11 0.01
Mon 10/12 19Z 0.31 3117  85  61  11 0.00
Mon 10/12 20Z 0.35 3118  89  65  10 0.01
Mon 10/12 21Z 0.34 3118  94  73   9 0.01
Mon 10/12 22Z 0.28 3216  95  74   8 0.01
Mon 10/12 23Z 0.22 3214  95  63   8 0.00
Tue 10/13 00Z 0.19 3213  95  64   8 0.00
Tue 10/13 01Z 0.14 3311  94  68   8 0.00
Tue 10/13 02Z 0.13 3208  93  84   8 0.01
Tue 10/13 03Z 0.12 3006  93  88   8 0.00
Tue 10/13 04Z 0.10 2904  93  93   8 0.00
Tue 10/13 05Z 0.05 2302  94  96   8 0.00
Tue 10/13 06Z 0.05 1906  96  96   8 0.02
Tue 10/13 07Z 0.06 1811  98  93   7 0.03
Tue 10/13 08Z 0.09 1817  98  94   7 0.03
Tue 10/13 09Z 0.12 1921  98  94   7 0.07
Tue 10/13 10Z 0.16 2023  98  91   8 0.06
Tue 10/13 11Z 0.19 2025  97  90  10 0.05
Tue 10/13 12Z 0.24 2126  97  88  10 0.06
Tue 10/13 13Z 0.25 2027  97  89  10 0.11
Tue 10/13 14Z 0.27 2128  96  89  10 0.12
Tue 10/13 15Z 0.28 2128  95  91  11 0.08
Tue 10/13 16Z 0.28 2128  95  94  12 0.05
Tue 10/13 17Z 0.31 2128  95  92  12 0.05

Run total areal avg QPF for the greens is: 1.09 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