The expressions General January (also, after French, General Janvier) and General February (also, after French, General Février, or General Fevrier) personify the winter months of January and February as army commanders—especially in reference to winter as detrimental or destructive to a military campaign.
—Cf. also General Winter.

The expression Generals Janvier and Fevrier occurs, for example, in United to stay ahead, by David Lacey, published in The Guardian (London and Manchester, England) of Saturday 3^rd April 1999—“Ferguson’s red army” designates Manchester United Football Club as managed by Alex Ferguson (born 1941):

When United reached the Champions League semi-finals the following season they also regained the title by taking 49 of their 75 points from their last 23 fixtures. Now 32 out of their total of 63 have come from the 10 wins and two draws since losing 3-2 at home to Middlesbrough on December 19. It is happening too often to be a coincidence. In the league Ferguson’s red army relies heavily on generals Janvier and Fevrier.

The texts containing the earliest occurrences of the expressions General January (also General Janvier) and General February (also General Février, or General Fevrier) seem to indicate that those expressions were coined by Prince Alexander Menshikov (1787-1869), who commanded the Russian army at the beginning of the Crimean War, i.e., the war fought from 1853 to 1856, mainly in Crimea, between Russia on one side and Turkey, France, Sardinia and Britain on the other.

The earliest occurrences of the expressions General January (also General Janvier) and General February (also General Février, or General Fevrier) that I have found are as follows:

1-: From a correspondence, in French, from Sebastopol, dated Sunday 7^th January 1855, published in the Courrier de Marseille (Marseille, Bouches-du-Rhône, France) of Tuesday 23^rd January 1855:

1.1-: As reprinted in the Journal des débats politiques et littéraires (Paris, France) of Thursday 25^th January 1855:

Le prince Menschikoff paraît décidé à ne plus entreprendre aucune action importante, soit que son armée, encore sous le coup de sa défaite d’Inkermann, ne se trouve pas en état, soit qu’il compte sur l’effet de la mauvaise saison pour affaiblir les alliés. Cette dernière opinion est assez répandue ; et a ce sujet on prête au commandant russe un propos caractéristique : « Que nos soldats se reposent, les généraux janvier, février et mars feront bien mieux nos affaires que toutes les attaques possibles. » Oui, ce sont bien là les auxiliaires sur lesquels la Russie a toujours le plus compté, car c ‘est à eux qu’elle doit ses succès les plus décisifs.

1.2-: As translated in The Sun (London, England) of Thursday 25^th January 1855:

Prince Menschikoff appears determined not to risk any general affair. Perhaps his army is still under the impression of its defeat at Inkerman, or he relies on the effects of the inclemency of the season on our soldiers. This last opinion is evidently entertained by the Russian General, who is reported to have said—‘Our troops may rest; Generals January, February, and March will fight their battles far better than they could.’ These are in reality the auxiliaries on which the Russians most confidently rely, for it is to them they are indebted for their most decisive successes.

2-: From The Standard (London, England) of Wednesday 24^th January 1855:

SIEGE OF SEBASTOPOL.
(From the Second Edition of the Morning Herald.)
(FROM OUR SPECIAL CORRESPONDENT.)

ENGLISH CAMP, HEIGHTS OF SEBASTOPOL, Jan. 1.
[…] The weather here, I am sorry to say, has changed sadly for the worse. Yesterday there was a heavy fall of snow, and for twenty-four hours previous it froze hard. Towards the middle of the day it became quite warm, and the snow and ice disappeared. To-day it is bitterly cold again. These sudden alterations of the temperature affect the health of our troops most seriously, and render the communication with Balaklava, if possible, even ten times more difficult than before. The appearance of the weather quite justified the remark which, whether rightly or wrongly, is attributed to Prince Mentschikoff, viz., that if the allies in their present condition withstood his three great generals, January, February, and March, they could resist anything. I almost fear to say how much truth there may be in such conjectures. […]
[…]
Jan. 4.
Everything still goes on slowly. All day yesterday and to-day the snow and hail has fallen incessantly. The whole surface of the ground, so far as I am able to judge by a 10 miles ride, is a complete half frozen quagmire. Our trenches and covered ways are mere ditches, filled with ice and water to the depth of three and four feet. Last night it rained until about four in the morning, when a heavy snow storm succeeded, which thawed in about half-an-hour, and flooded the camp. Mentschikoff seems to have had good reason when he relied upon his three generals, January, February, and March. Our men would laugh at the weather if they were only hutted; but under tents and only clad in their great coats, they suffer severely.

3-: From “the last intelligence from the seat of war in the Crimea”, published in The Morning Chronicle (London, England) of Thursday 25^th January 1855:

However severe may be the sufferings of the allied armies, they are greatly surpassed by those which have befallen the soldiers of the Czar. The Generals January, February, and March, on whose alliance Prince Menschikoff is stated to have expressed such boasting confidence, may perhaps prove to him but sorry traitors. What misery can surpass that experienced by the Russian battalion on their terrible march from Odessa to the distant lines of Perekop! Hundreds are described as perishing on the way from hunger and exhaustion, whilst of the survivors a large percentage arrived at their destination incapacitated and dying.

4-: From The Times (London, England) of Monday 12^th February 1855:

THE WAR.
THE SIEGE OF SEBASTOPOL.
(FROM OUR SPECIAL CORRESPONDENT.)

CAMP BEFORE SEBASTOPOL, Jan. 27.
The weather, thanks to Heaven, continues to be extremely favourable to us. Cold, clear nights, with a bright, unclouded moon, are followed by warm, sunny, genial days. The thermometer generally falls to 18° or 20° at 12 every night, and rises to 44° of Fahrenheit at noon the following day. So far Prince Menschikoff has not received the assistance which he is reported to have expected from “Son bon Général Janvier,” and we can only anxiously pray that the aid he looks for from his other confrère, “General Fevrier,” may be equally insignificant and unsubstantial. It is not unusual to have several weeks of fine weather of this kind at a corresponding period of the year in the Crimea, but all the natives concur in stating that we have still hard times before us—tempest, heavy rains, or snow, but not very intense cold, and that this introduction to the Crimean spring continues on an average for about three weeks, but that it may last twice as long.

5-: From the caption to the following cartoon by the British caricaturist and illustrator John Leech (1817-1864), published in Punch, or the London Charivari (London, England) of Saturday 10^th March 1855:
—This cartoon depicts General Février as a skeleton general, standing at the bedside of Tsar Nicholas I, who died on 18^th February [2^nd March, New Style] 1855:

“GENERAL FÉVRIER” TURNED TRAITOR.

“Russia has Two Generals in whom she can confide—Generals Janvier and Février.”—Speech of the late Emperor of Russia.