NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260202_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)
=== ===== === ==== ==== === === === ====
Mon 02/02 06Z 0.04 3425  66  23 -10 0.00
Mon 02/02 07Z 0.04 3429  58  24  -8 0.00
Mon 02/02 08Z 0.02 3429  51  26  -8 0.00
Mon 02/02 09Z 0.02 3429  47  27  -8 0.00
Mon 02/02 10Z 0.03 3428  46  27  -8 0.00
Mon 02/02 11Z 0.02 3427  45  25  -8 0.00
Mon 02/02 12Z 0.02 3426  45  22  -8 0.00
Mon 02/02 13Z 0.02 3425  45  19  -9 0.00
Mon 02/02 14Z 0.02 3423  43  17  -9 0.00
Mon 02/02 15Z 0.02 3422  42  14  -9 0.00
Mon 02/02 16Z 0.04 3421  41  13  -9 0.00
Mon 02/02 17Z 0.04 3421  38  12  -9 0.00
Mon 02/02 18Z 0.07 3421  38  12  -9 0.00
Mon 02/02 19Z 0.11 3323  40  11  -9 0.00
Mon 02/02 20Z 0.14 3324  42  11  -9 0.00
Mon 02/02 22Z 0.16 3322  44  12  -9 0.00
Mon 02/02 23Z 0.15 3322  42  15  -9 0.00
Tue 02/03 00Z 0.13 3321  41  23  -8 0.00
Tue 02/03 01Z 0.08 3320  40  41  -8 0.00
Tue 02/03 02Z 0.05 3418  39  56  -8 0.00
Tue 02/03 03Z 0.04 3416  41  54  -8 0.00
Tue 02/03 04Z 0.06 3314  41  52  -8 0.00
Tue 02/03 05Z 0.07 3312  42  51  -8 0.00
Tue 02/03 06Z 0.10 3211  41  53  -8 0.00
Tue 02/03 07Z 0.14 3112  40  55  -8 0.00
Tue 02/03 08Z 0.15 3011  39  53  -8 0.00
Tue 02/03 09Z 0.17 2910  40  49  -9 0.00
Tue 02/03 10Z 0.16 2808  40  25  -9 0.00
Tue 02/03 11Z 0.15 2807  40  10  -9 0.00
Tue 02/03 12Z 0.15 2807  41  13  -9 0.00
Tue 02/03 13Z 0.16 2707  43  16  -9 0.00
Tue 02/03 14Z 0.16 2607  43  20  -9 0.00
Tue 02/03 15Z 0.19 2508  45  65  -9 0.00
Tue 02/03 16Z 0.21 2408  50  90 -10 0.00
Tue 02/03 17Z 0.26 2409  63  90 -10 0.00
Tue 02/03 18Z 0.32 2409  76  85 -11 0.00
Tue 02/03 19Z 0.36 2309  83  67 -11 0.00
Tue 02/03 20Z 0.42 2310  87  29 -12 0.00
Tue 02/03 21Z 0.40 2410  89  24 -12 0.00
Tue 02/03 22Z 0.40 2511  92  37 -12 0.00
Tue 02/03 23Z 0.50 2513  95  51 -13 0.00
Wed 02/04 00Z 0.60 2515  95  72 -13 0.00
Wed 02/04 01Z 0.64 2616  94  76 -13 0.01
Wed 02/04 02Z 0.63 2616  92  75 -13 0.01
Wed 02/04 03Z 0.64 2716  91  68 -14 0.00
Wed 02/04 04Z 0.65 2716  90  51 -14 0.00
Wed 02/04 05Z 0.67 2716  91  37 -14 0.00
Wed 02/04 06Z 0.56 2816  92  34 -14 0.01
Wed 02/04 07Z 0.57 2816  92  38 -15 0.00
Wed 02/04 08Z 0.71 2817  91  43 -16 0.00
Wed 02/04 09Z 0.70 2717  91  36 -16 0.00
Wed 02/04 10Z 0.65 2818  92  35 -17 0.00
Wed 02/04 11Z 0.45 2918  86  36 -17 0.00
Wed 02/04 12Z 0.31 3118  80  37 -16 0.00
Wed 02/04 13Z 0.27 3118  80  37 -15 0.00
Wed 02/04 14Z 0.26 3117  80  38 -15 0.00
Wed 02/04 15Z 0.25 3116  81  35 -15 0.00
Wed 02/04 16Z 0.25 3115  81  34 -14 0.00
Wed 02/04 17Z 0.29 3014  82  34 -14 0.00

Run total areal avg QPF for the Central_Greens is: 0.03 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