NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260908_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 09/08 06Z 0.18 3314  80  45  10 0.00
Tue 09/08 07Z 0.22 3316  80  47  10 0.00
Tue 09/08 08Z 0.22 3316  80  54  10 0.00
Tue 09/08 09Z 0.28 3214  79  55  10 0.00
Tue 09/08 10Z 0.38 3114  79  60  10 0.00
Tue 09/08 11Z 0.51 3015  81  68  10 0.00
Tue 09/08 12Z 0.60 2916  83  70   9 0.00
Tue 09/08 13Z 0.57 3018  87  78   9 0.00
Tue 09/08 14Z 0.41 3117  89  82   9 0.00
Tue 09/08 15Z 0.33 3114  86  87  10 0.00
Tue 09/08 16Z 0.32 3113  86  83  10 0.00
Tue 09/08 17Z 0.34 3114  88  88  10 0.01
Tue 09/08 18Z 0.29 3113  91  74  10 0.00
Tue 09/08 19Z 0.24 3112  94  71  10 0.00
Tue 09/08 20Z 0.20 3212  96  58  10 0.00
Tue 09/08 21Z 0.14 3209  95  45  10 0.00
Tue 09/08 22Z 0.15 3108  94  33  10 0.00
Tue 09/08 23Z 0.11 3207  91  44  10 0.00
Wed 09/09 00Z 0.09 3105  86  34  11 0.00
Wed 09/09 01Z 0.10 3004  85  19  11 0.00
Wed 09/09 02Z 0.11 2703  85   8  11 0.00
Wed 09/09 03Z 0.12 2404  88   6  10 0.00
Wed 09/09 04Z 0.14 2305  92   6  10 0.00
Wed 09/09 05Z 0.17 2207  95   5  10 0.00
Wed 09/09 06Z 0.20 2209  97   7  11 0.01
Wed 09/09 07Z 0.24 2111  99   8  11 0.01
Wed 09/09 08Z 0.28 2212  97  20  11 0.01
Wed 09/09 09Z 0.27 2212  95  68  11 0.01
Wed 09/09 10Z 0.28 2212  94  61  11 0.01
Wed 09/09 11Z 0.37 2214  96  52  11 0.01
Wed 09/09 12Z 0.40 2314  95  54  11 0.00
Wed 09/09 13Z 0.45 2217  94  61  11 0.00
Wed 09/09 14Z 0.47 2219  89  62  12 0.00
Wed 09/09 15Z 0.41 2218  81  56  13 0.00
Wed 09/09 16Z 0.49 2221  75  48  12 0.00
Wed 09/09 17Z 0.49 2220  80  39  12 0.01
Wed 09/09 18Z 0.46 2122  87  36  12 0.01
Wed 09/09 19Z 0.54 2123  95  51  12 0.01
Wed 09/09 20Z 0.53 2124  89  86  13 0.03
Wed 09/09 21Z 0.52 2026  92  88  13 0.04
Wed 09/09 22Z 0.63 2034  96  90  14 0.05
Wed 09/09 23Z 0.77 2135  97  89  14 0.04
Thu 09/10 00Z 0.87 2236  97  89  15 0.03
Thu 09/10 01Z 0.96 2237  97  82  15 0.03
Thu 09/10 02Z 1.04 2338  97  73  15 0.04
Thu 09/10 03Z 1.02 2338  97  64  15 0.07
Thu 09/10 04Z 1.06 2339  96  61  15 0.03
Thu 09/10 05Z 1.02 2338  97  70  15 0.04
Thu 09/10 06Z 1.09 2339  97  84  15 0.06
Thu 09/10 07Z 1.01 2438  97  95  15 0.09
Thu 09/10 08Z 1.00 2438  98  89  16 0.12
Thu 09/10 09Z 1.00 2534  98  62  15 0.09
Thu 09/10 10Z 0.93 2628  95  42  14 0.03
Thu 09/10 11Z 0.99 2727  92  29  13 0.02
Thu 09/10 12Z 1.02 2727  90  34  12 0.02
Thu 09/10 13Z 1.09 2728  85  31  12 0.01
Thu 09/10 14Z 1.18 2727  83  23  11 0.01
Thu 09/10 15Z 1.63 2725  82  26  11 0.00
Thu 09/10 16Z 5.90 2724  77  15  10 0.00
Thu 09/10 17Z 12.68 2722  72  12  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.95 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