NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260928_1200
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)
=== ===== === ==== ==== === === === ====
Mon 09/28 12Z 0.45 0817  95  97   8 0.00
Mon 09/28 13Z 0.45 0818  95  98   8 0.01
Mon 09/28 14Z 0.42 0916  97  97   7 0.01
Mon 09/28 15Z 0.35 0914  97  88   8 0.01
Mon 09/28 16Z 0.31 0912  96  84   8 0.01
Mon 09/28 17Z 0.25 0910  97  83   8 0.01
Mon 09/28 18Z 0.19 0907  97  87   8 0.01
Mon 09/28 19Z 0.16 0806  98  85   8 0.01
Mon 09/28 20Z 0.15 0706  98  85   8 0.01
Mon 09/28 21Z 0.16 0607  97  86   9 0.01
Mon 09/28 22Z 0.16 0607  98  86   9 0.01
Mon 09/28 23Z 0.17 0508  98  87   9 0.01
Tue 09/29 00Z 0.15 0507  97  85   9 0.01
Tue 09/29 01Z 0.11 0406  97  83   9 0.01
Tue 09/29 02Z 0.05 0106  98  85   9 0.00
Tue 09/29 03Z 0.03 0006  98  87   9 0.00
Tue 09/29 04Z 0.02 0007  98  88   9 0.00
Tue 09/29 05Z 0.03 3509  98  90   9 0.00
Tue 09/29 06Z 0.03 3510  97  91   9 0.00
Tue 09/29 07Z 0.04 3511  96  92   9 0.00
Tue 09/29 08Z 0.04 3511  96  90  10 0.00
Tue 09/29 09Z 0.04 0011  94  85  10 0.00
Tue 09/29 10Z 0.04 3512  94  83  10 0.00
Tue 09/29 11Z 0.05 3513  95  83  10 0.00
Tue 09/29 12Z 0.05 3513  96  84   9 0.01
Tue 09/29 13Z 0.06 0013  96  84   9 0.01
Tue 09/29 14Z 0.06 0012  96  83   9 0.01
Tue 09/29 15Z 0.06 0012  95  81   9 0.00
Tue 09/29 16Z 0.05 3513  95  80   9 0.00
Tue 09/29 17Z 0.04 3514  95  78   9 0.01
Tue 09/29 18Z 0.04 3514  95  77   9 0.01
Tue 09/29 19Z 0.04 0013  94  72   9 0.00
Tue 09/29 20Z 0.06 0112  91  63  10 0.00
Tue 09/29 21Z 0.06 0113  90  57  10 0.00
Tue 09/29 22Z 0.03 0014  91  59   9 0.00
Tue 09/29 23Z 0.03 0014  89  60   9 0.01
Wed 09/30 00Z 0.04 0013  87  53  10 0.00
Wed 09/30 01Z 0.04 0011  87  47  10 0.00
Wed 09/30 02Z 0.07 0110  86  42  10 0.00
Wed 09/30 03Z 0.04 0108  87  38   9 0.00
Wed 09/30 04Z 0.03 0006  85  33  10 0.00
Wed 09/30 05Z 0.02 0005  84  29  10 0.00
Wed 09/30 06Z 0.02 3505  84  23  10 0.00
Wed 09/30 07Z 0.06 3306  84  21  10 0.00
Wed 09/30 08Z 0.08 3206  81  20  10 0.00
Wed 09/30 09Z 0.07 3307  78  18  10 0.00
Wed 09/30 10Z 0.06 3307  74  15  11 0.00
Wed 09/30 11Z 0.07 3307  70  15  11 0.00
Wed 09/30 12Z 0.06 3305  66  16  11 0.00
Wed 09/30 13Z 0.07 3206  64  21  11 0.00
Wed 09/30 14Z 0.06 3205  61  26  12 0.00
Wed 09/30 15Z 0.07 3104  61  33  11 0.00
Wed 09/30 16Z 0.11 2905  62  38  11 0.00
Wed 09/30 17Z 0.13 2805  63  35  11 0.00
Wed 09/30 18Z 0.14 2806  61  28  11 0.00
Wed 09/30 19Z 0.14 2705  59  23  11 0.00
Wed 09/30 20Z 0.18 2606  58  21  11 0.00
Wed 09/30 21Z 0.21 2707  53  26  11 0.00
Wed 09/30 22Z 0.28 2710  57  38  11 0.00
Wed 09/30 23Z 0.29 2711  67  36  11 0.00

Run total areal avg QPF for the greens is: 0.19 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