NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260407_0600
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)
=== ===== === ==== ==== === === === ====
Tue 04/07 06Z 0.37 2708  82  72  -8 0.00
Tue 04/07 07Z 0.38 2607  79  71  -8 0.00
Tue 04/07 08Z 0.33 2406  79  69  -8 0.00
Tue 04/07 09Z 0.26 2107  80  74  -8 0.00
Tue 04/07 10Z 0.24 2108  86  79  -7 0.00
Tue 04/07 11Z 0.11 1906  88  83  -7 0.00
Tue 04/07 12Z 0.03 1708  92  85  -7 0.01
Tue 04/07 13Z 0.03 1712  95  88  -7 0.04
Tue 04/07 14Z 0.10 1815  96  84  -7 0.06
Tue 04/07 15Z 0.28 2012  97  87  -7 0.03
Tue 04/07 16Z 0.50 2212  99  75  -7 0.02
Tue 04/07 17Z 1.66 2515  97  80  -7 0.03
Tue 04/07 18Z 1.82 2517  97  77  -7 0.01
Tue 04/07 19Z 2.24 2619  95  68  -7 0.02
Tue 04/07 20Z 0.84 3026  96  64  -9 0.04
Tue 04/07 21Z 0.41 3230  91  77 -10 0.03
Tue 04/07 22Z 0.48 3131  88  59 -11 0.01
Tue 04/07 23Z 0.58 3130  89  17 -12 0.00
Wed 04/08 00Z 0.67 3129  90   9 -12 0.00
Wed 04/08 01Z 0.58 3127  80  18 -12 0.00
Wed 04/08 02Z 0.61 3227  72  25 -12 0.00
Wed 04/08 03Z 0.52 3226  68  21 -13 0.00
Wed 04/08 04Z 0.41 3224  57  20 -12 0.00
Wed 04/08 05Z 0.33 3222  48  21 -12 0.00
Wed 04/08 06Z 0.29 3221  46  22 -12 0.00
Wed 04/08 07Z 0.26 3220  46  21 -12 0.00
Wed 04/08 08Z 0.24 3219  43  19 -11 0.00
Wed 04/08 09Z 0.22 3219  40  21 -10 0.00
Wed 04/08 10Z 0.19 3217  38  18 -10 0.00
Wed 04/08 11Z 0.18 3116  37  14  -9 0.00
Wed 04/08 12Z 0.17 3113  36  12  -8 0.00
Wed 04/08 13Z 0.16 3011  35  10  -8 0.00
Wed 04/08 14Z 0.17 2909  33   8  -7 0.00
Wed 04/08 15Z 0.18 2808  31   5  -6 0.00
Wed 04/08 16Z 0.19 2807  27   3  -6 0.00
Wed 04/08 17Z 0.21 2706  24   3  -5 0.00
Wed 04/08 18Z 0.27 2706  22   4  -5 0.00
Wed 04/08 19Z 0.42 2504  22   4  -5 0.00
Wed 04/08 20Z 0.49 2304  22   5  -4 0.00
Wed 04/08 21Z 0.48 2206  22   7  -4 0.00
Wed 04/08 22Z 0.29 2207  22   8  -3 0.00
Wed 04/08 23Z 0.27 2110  20   9  -3 0.00
Thu 04/09 00Z 0.30 2113  17   8  -2 0.00
Thu 04/09 01Z 0.33 2116  14   9  -1 0.00
Thu 04/09 02Z 0.37 2218  14   9   0 0.00
Thu 04/09 03Z 0.37 2219  19   8   0 0.00
Thu 04/09 04Z 0.35 2220  23   9   0 0.00
Thu 04/09 05Z 0.34 2221  24  16   1 0.00
Thu 04/09 06Z 0.33 2122  25  35   1 0.00
Thu 04/09 07Z 0.34 2123  20  49   2 0.00
Thu 04/09 08Z 0.36 2124  16  56   2 0.00
Thu 04/09 09Z 0.38 2125  12  58   3 0.00
Thu 04/09 10Z 0.40 2126  10  56   3 0.00
Thu 04/09 11Z 0.43 2128   7  52   3 0.00
Thu 04/09 12Z 0.44 2129   6  49   3 0.00
Thu 04/09 13Z 0.45 2130   6  50   3 0.00
Thu 04/09 14Z 0.45 2130   5  50   4 0.00
Thu 04/09 15Z 0.46 2129   6  47   4 0.00
Thu 04/09 16Z 0.47 2128   8  48   4 0.00
Thu 04/09 17Z 0.51 2127  11  46   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.30 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