NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260601_1800
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)
=== ===== === ==== ==== === === === ====
Mon 06/01 18Z 1.19 0204  79  67   3 0.00
Mon 06/01 19Z 0.87 0104  76  60   4 0.01
Mon 06/01 20Z 0.64 0104  76  56   4 0.01
Mon 06/01 21Z 0.29 0003  77  57   4 0.01
Mon 06/01 22Z 0.18 3503  78  57   4 0.01
Mon 06/01 23Z 0.07 3402  79  60   4 0.01
Tue 06/02 00Z 0.09 3303  79  55   4 0.01
Tue 06/02 01Z 0.07 3406  77  52   4 0.00
Tue 06/02 02Z 0.04 3408  74  53   4 0.00
Tue 06/02 03Z 0.05 3509  71  46   4 0.00
Tue 06/02 04Z 0.10 3510  69  41   4 0.00
Tue 06/02 05Z 0.15 3511  68  37   4 0.00
Tue 06/02 06Z 0.13 3510  67  32   4 0.00
Tue 06/02 07Z 0.15 3309  68  33   4 0.00
Tue 06/02 08Z 0.27 3109  69  38   4 0.00
Tue 06/02 09Z 0.36 3011  67  44   4 0.00
Tue 06/02 10Z 0.39 3013  66  46   5 0.00
Tue 06/02 11Z 0.33 3215  63  43   5 0.00
Tue 06/02 12Z 0.24 3216  62  32   5 0.00
Tue 06/02 13Z 0.23 3215  60  24   5 0.00
Tue 06/02 14Z 0.25 3316  55  17   6 0.00
Tue 06/02 15Z 0.29 3317  51  10   6 0.00
Tue 06/02 16Z 1.38 3318  49   5   6 0.00
Tue 06/02 17Z 1.97 3319  47   6   6 0.00
Tue 06/02 18Z 2.45 3320  45  12   6 0.00
Tue 06/02 19Z 2.65 3320  48  21   6 0.00
Tue 06/02 20Z 2.61 3319  52  41   6 0.00
Tue 06/02 21Z 1.84 3319  53  59   7 0.00
Tue 06/02 22Z 0.79 3320  55  75   7 0.00
Tue 06/02 23Z 0.24 3422  55  77   7 0.00
Wed 06/03 00Z 0.14 3423  53  63   7 0.00
Wed 06/03 01Z 0.11 3422  53  44   7 0.00
Wed 06/03 02Z 0.09 3521  52  39   7 0.00
Wed 06/03 03Z 0.17 3519  50  30   7 0.00
Wed 06/03 04Z 0.23 0017  46  25   8 0.00
Wed 06/03 05Z 0.29 0016  43  12   8 0.00
Wed 06/03 06Z 0.22 0014  42  11   8 0.00
Wed 06/03 07Z 0.16 3514  43  11   8 0.00
Wed 06/03 08Z 0.16 3514  43  17   8 0.00
Wed 06/03 09Z 0.15 3513  44  27   8 0.00
Wed 06/03 10Z 0.07 3513  45  38   8 0.00
Wed 06/03 11Z 0.09 3513  44  46   8 0.00
Wed 06/03 12Z 0.06 3511  44  44   8 0.00
Wed 06/03 13Z 0.06 3409  45  60   8 0.00
Wed 06/03 14Z 0.20 3309  47  70   8 0.00
Wed 06/03 15Z 0.32 3209  48  76   9 0.00
Wed 06/03 16Z 0.89 3210  48  76   9 0.00
Wed 06/03 17Z 1.42 3211  47  76   9 0.00
Wed 06/03 18Z 1.48 3210  46  75  10 0.00
Wed 06/03 19Z 1.55 3109  48  70  10 0.00
Wed 06/03 20Z 1.38 3109  50  66  10 0.00
Wed 06/03 21Z 0.83 3110  53  61  11 0.00
Wed 06/03 22Z 0.52 3009  55  57  11 0.00
Wed 06/03 23Z 0.47 2909  57  52  11 0.00
Thu 06/04 00Z 0.46 2809  59  47  11 0.00
Thu 06/04 01Z 0.46 2809  58  40  11 0.00
Thu 06/04 02Z 0.47 2810  59  38  11 0.00
Thu 06/04 03Z 0.42 2910  60  37  11 0.00
Thu 06/04 04Z 0.33 3010  60  34  11 0.00
Thu 06/04 05Z 0.30 3010  58  31  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.06 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